The South Staffordshire Coalfield/Chapter 12
CHAPTER XII.
The Boundary Faults and the Rocks surrounding the Coal-Field.
We will now examine the east and west boundaries of the coalfield. One difference between these and the north and south boundaries will strike us at the first glance of the map. Instead of being irregularly and deeply indented, and conforming to the natural surface of the ground, advancing or receding with its hills and valleys, the cast and west boundaries are regular and equable, preserving a certain mean course with great persistency, and when curving, doing so gradually, and with a wide and steady sweep, forming a curve of large radius. The north and south boundaries are like an indented coast line, the east and west are like artificial roads, going nearly straight across the country, with but little respect to the variations in its surface. These boundaries, indeed, are not the result of mere denudation alone (or of that action by which the present configuration of the surface has been produced), but of denudation combined with great longitudinal faults, which at the very period of their formation produced a sudden change in the ground along their line, so that no subsequent lowering of the level of the ground, though it may slightly shift the position, can much alter the character of that change. This difference in the nature of the two boundaries has a very important practical bearing. When the boundary of a coal field has been formed by simple denudation, without any faults in the neighbourhood, we can follow the beds of coal under the other rock without much regarding it; it is simply an additional matter of so much thickness interposed between the surface and the bed, and if the dip of of the two rocks be known, and the surface be levelled, the depth of the coal can be calculated with the greatest facility. When, however, the boundary of a coal-field is caused by a fault, the mere dip of the rocks is no longer a trustworthy guide to us. The "throw" of the fault, as also the angle of its inclination, or "hade," is à priori unknown to us; we have therefore commonly no means of judging how far the coal-bed is depressed on the other side of the fault below its level on this, and if we knew that, we should perhaps have no means of ascertaining how far the fault "haded," "overhung," or "inclined;" or, in other words, how far we ought to go beyond the broken end of coal on this side of the fault, before we felt sure that we were standing over the other end of the bed on the other side of the fault.
The determination of the nature and character of the boundary faults of the coal-fields, therefore, is one of the most important practical points which it is the province and the duty of a Geological survey to solve, since it is one of those least within the power of on individual observer, examining only small and isolated localities, to understand and explain.
I was at one time strongly inclined to entertain the supposition that the boundary faults of the Midland coal-fields were of the nature of cliffs rather than of fractures. It appeared from certain circumstances rather probable that the previously existing Coal-measures had been almost entirely destroyed and washed away, except in the parts where they are now seen at the surface; that in those parts they had been left as islands, round which the beds of the Permian and New red sandstone had been deposited, abutting against the old Coal-measure cliffs, their beds taking the place of those that had been swept away. Facts such as those we have seen in the Brereton district, where the coal cropped up into the New red sandstone, without the intervention of any fault, lent strength to this hypothesis. Soon after the commencement of the survey of the South Staffordshire Coal-field, however, my belief in this hypothesis was greatly shaken, and it was finally abandoned, so far as the supposition of any long line of lofty cliff was concerned, having a more or less nearly perpendicular face, with several hundred feet of New red sandstone deposited against it. The very form of the east and west boundary faults of this coal-field was against this supposition. Direct evidence against it, as to the West Bromwich district at all events, was soon obtained, and all doubt was finally set at rest when the boundary between the New red sandstone and Permian formations was surveyed. For it then appeared that sometimes a broad tract of Permian rock lay next outside the boundary fault, sometimes none at all. If, therefore, the gap caused by the supposed denudation of the Coal-measures had been first of all filled up by Permian, it would follow that that formation itself had subsequently suffered an almost equal amount of destruction, and another great cliff formed; and that in some places the whole of the Permian formation had been utterly removed, and the old Coal-measure cliff re-exposed, only to be again concealed and the second gap filled up by subsequently-formed beds of New red sandstone. Such a recurrence of so singular a phenomenon was too much for the wildest hypothesis to affirm; and we shall. I think, see reason to conclude that the east and west boundaries of the coal-field are not only genuine faults, clean-cut fractures, but that they were produced late in the New red sandstone period, if not subsequently to it altogether.
The practical bearing of this discussion will be at once seen, if we reflect that on the first supposition of the boundaries being cliffs, a very large part of the Coal-measures, with their accompanying wealth of coal and iron, must have been removed from the spaces between our present coal-fields; if, on the other hand, the boundaries are faults, we have still all or the greater part of the Coal-measures concealed and untouched under the New red sandstone of the great central plain of England.
We will now examine a little in detail these two boundary faults, commencing with the eastern one near its southern extremity on the Birmingham and Halesowen road.
The Eastern Boundary fault.—At Perry Hill the angular trappean breccia of the Permian rocks is seen in the cutting of the road, the Red rock extending up to the turnpike. Near the Hagge, Round Hill, and "Barn," yellow Coal-measure sandstone may be seen. Just where "ra" of "Brand Hall" is in the map is an old quarry in the calcareous conglomerate, described before as occurring in the Permian rocks. This band of calcarcous conglomerate can be traced thence to Barnford Hill, where it is much farther from the fault than it was at Brand Hall. This looks as if the fault increased in amount as it ran south, concealing more and more of the Permian rocks, and thus bringing this conglomerate bed nearer and nearer to it.
About 350 yards south-west of Langley mill there is an old pit only 130 yards (390 feet) deep, which, from the quantity of Silurian shale full of fossils on the bank, must have had almost the whole of its lower half altogether in that formation.[1] This is very near the boundary fault, but how the Silurian shale comes to be so near to the surface as even 100 yards is not easy to explain. From some old mining plans of this locality lent to me by Mr. S. H. Blackwell there appeared to have been here a curious complication of faults, the clue to which I did not succeed in unravelling. A little north of this, in Mr. Chance's pits, the Thick coal thinned out to 7 feet as it approached the fault. Red rock can be seen at the surface very near the line of the fault as it is drawn on the map. It is probable, then, that there is here a complication similar to that described before in Lord Dartmouth's Heath pits at West Bromwich.[2]
North of Oldbury the fault is very well traced. At the Flash we have the Thick coal 60 yards (180 feet) deep on one side, and 212 yards (636 feet) on the other, giving a downthrow of 152 yards (456 feet); but the amount of "red rock" sunk through was not known. At Mr. Bennett's pits at Ireland Green the Thick coal is 170 yards (510 feet) deep, while on the other side of the fault, near "the Oaks," it is 288 yards (864 feet), giving a downthrow of 118 yards (354 feet). At the Terrace pits at Christchurch the Thick coal is 252 yards (756 feet) deep, and it was said to be only 45 yards (135 feet) to the bottom of the "red rock," the downthrow of the fault being 88 yards (264 feet). This fault continues to hold its course to the northward for a mile beyond this point, having still a downthrow to the east of 60 or 80 yards (110 to 240 feet), till it appears to be cut off by the Tipton and Hilltop fault. North of the Cross Guns Inn, however, in the Wolverhampton and Birmingham road, it is no longer the boundary of the coal-field even at the surface, as there is no red rock on either side of it. At a new pit sunk about the foot of the "L" of "Lyndon" in the Ordnance map they sank below the Broach coal without meeting with any red rock. From the depth of the Broach here it will be about 200 yards (600 feet) to the Thick coal. About one-third of a mile to the south of this spot is the Lewisham pit, at which the Thick coal is 290 yards (870 feet) deep, and there is said to be 105 yards (315 feet) of red rock above the Coal-measures. It is doubtful whether there be a fault, downcast to the south, between these two points, or whether the lower level of the Thick coal at the Lewisham pits is due merely to the southerly dip of those from Lyndon. A dip of 10° would be sufficient for the purpose. If there be no fault, the Permian red rock must come in either by simple capping of the Coal-measures, or it may have been originally deposited in a sudden hollow of erosion existing formerly in the Coal-measures of that locality. East of Lyndon and north of the "red rock" the Thick coal is said to end at a depth of 200 yards (600 feet) against-a mass of "rock and rig." This is probably an extension of the "rock fault" found both in the "Heath" and "Lewisham" pits as before described.
From this point we have to traverse a district of very great obscurity for two or three miles. A ridge of drift gravel runs from Sandwell park by West Bromwich old church to Charleymount. This drift is in some places 120 feet thick, and effectually screens all the rocks below from observation. At a small public house between Bird End and the Wigmoor station gas escapes from the ground in such quantity that it is used to light the house and the neighbouring cottages. It is almost certain, then, that there are Coal-measures under this spot, though they can only contain the lowest beds of coal. In the cutting of the railway to the north-east of Crank Hall farm Silurian shale full of fossils was found lying horizontally.
In the road going from Wigmoor station to Newtown, red rock may be observed apparently horizontal. "Red rock" spreads from this point over all the country to the north and east. Trusting to these facts, a dotted or supposed fault has been drawn from the Cross Guns to Sunday Bridge. From this point towards the north we have on one side of a certain line running about north-by-east. Silurian shale dipping very slightly to the south; and on the other side, red rock, which, whenever it is exposed, is found to have an easterly dip.
On the Walsall and Birmingham road, as we rise from the Silurian flat about the Bell, on to the gentle elevation on which the Gough's Arms stands, we meet first with some pale wine-coloured mottled calcareous sandstone, above which, in a brick pit, we find some grey and mottled clays and marls, with interstratified sandstone bands, that dip apparently east-south-east at 40°. Over these in a field opposite the Gough's Arms is a band of the calcareous conglomerate, just the same as that of Barnford Hill before described, dipping cast-south-east at 20°. These are all evidently Permian beds. On the higher ground, where "Quarry" and "Snail's Green" is engraved in the Ordnance map, we find a large gravel-pit opened in the quartzose conglomerates forming the base of the New red sandstone.
Further north we get red sandstone and marl, probably Permian, on a level with the Barr limestone near "the Skip," and following on to the east of Hay Head we find red rocks to the east of a certain curved line, while there are Silurian and Coal-measures on the west of it. The way in which the two little bits of Llandovery sandstone are allowed to peep out at Shustoke Lodge and behind Daffodilly, while over the intermediate space the Wenlock shale appears to come directly against the red rock, may be explained on the supposition that the fault here is a waved and gently indented line, and that as the Silurian beds crop towards the east, when the fault makes an eastward bend, it allows the lower rock to crop out, while when it bends to the west it cuts into higher beds, and of course prevents the outcrop of the lower.
So far I have endeavoured simply to describe facts, and give their most obvious explanation. Still it cannot be denied that there is something yet to be learnt respecting the nature of the boundary of the coal-field between Hay Head and Lappal. We may readily allow the boundary between the red rocks (taking Permian and New red sandstone together) on the one side, and the Silurian and Coal-measures on the other, to be an ordinary fault with a large downthrow to the east all the way from Hay Head south to Sunday Bridge. But we are then driven to the supposition that it splits, and that of the two branches into which it divides, one soon ends in the red rocks, and the other goes on at right angles to the former course[3] until it meets another fault running parallel to the first, and likewise forming a boundary between the red rocks and the Coal-measures. Now there is, in fact, little or no evidence for this splitting of the boundary fault, and we cannot at all satisfactorily account for the southern termination of the part of it that runs by Barr.
Again, the fault running by Oldbury is certainly a large downthrow to the east, and it certainly forms the boundary line between the red rocks and the Coal-measures at the surface, but it can hardly be called the boundary of the coal-field, inasmuch as the coals are got for a mile or more to the east of it, at only a comparatively slight increase of depth. Not only so, but the Coal-measures appear even at the surface on the eastern side of this fault, both north of the red rocks towards West Bromwich, and southwards towards Wilderness Farm and the Stone House. That this appearance of Coal-measures is due to cross faults cutting off the red rocks in each direction is at present a mere arbitrary and gratuitous supposition, though it is perhaps the most probable explanation of the facts that can at present be given.
Mr. Hull examined and determined the boundaries of the New red sandstone from Hampstead Hill through Smethwick and Harborne, and arrived at the conclusion that the boundary between the New red and that considered to be Permian was not a fault but a natural boundary, a conclusion in which Professor Ramsay believes him to be correct.
We are, therefore, left to mere conjecture as to the lie and position of the Coal-measures below the red rocks east of the line up to which they have been worked.
It will be more convenient now if we go to the northern end of the eastern boundary fault and trace it southwards. In the Brereton colliery they drove through the fault, and found some part of the conglomerates of the New red against the fifteenth coal at a depth of 460 feet. New red conglomerates rest upon the Coal-measures here on the western side of the field without the intervention of any fault, but it does not follow that they are the same beds of conglomerate, and it is quite possible that those found at this depth in the workings are much higher in the series than those found at the surface at Stile Cop and the neighbourhood. The downthrow of the fault, therefore, may be a great deal more than that 460 feet, and there may be a succession of step-like downthrows outside it again. One such step-like downthrow was observed in a gravel pit at no great distance from the spot. Starting from this point along the line drawn on the map to the southward, we have abundant evidence of "Red rock" on one side, and of Coal-measures on the other, lying just below the surface of the ground in a nearly horizontal position. The Red rock is the ordinary Red sandstone of the New red formation. In Beaudesert Park it is apparently one of the soft red sandstones that were formerly called Brick red sandstone; about Cannock Wood the beds are white and brown sandstones, and on Old Lodge Hill are some excavations in red marl that appear to be just the bottom beds of the upper subdivision of the formation, the Red marls. From this point scarcely anything can be seen or known for about two miles, till we arrive at the Hammerwich colliery just east of the dam of the reservoir. In the coal-pits there they drove to the east, and struck the Red rock fault just under where the feeder falls into the new branch of the canal. The Red rock is seen in the canal to be the lower subdivision of the New red sandstone, consisting of Red sandstones and conglomerates, and the coals are known to be in the lowest portion of the Coal-measures. So far we have seen no Permian rocks, though it is quite possible that rocks of that formation lie concealed under the New red sandstone, and between it and the Coal-measures on the downcast sido of the great fault.
Nevertheless, no rock considered to be Permian makes its appearance at the surface between the New red sandstone and the lower rocks, till we come south of Aldridge to the neighbourhood of Hay Head and Great Barr, which has been before described.
Somewhere about the Brown Hill, however, it would appear that a split takes place in the boundary fault, and that a branch is sent off into the Coal-measures, ranging down the valley by Clayhanger, and thence to the southward, until it probably meets with or passes into the Linley and Daw End fault that cuts off the Walsall Silurian rocks.
The bottom Coal-measures crop, as before shown, all along the region of Pelsall Heath and the Brown Hills, dipping to the west. East of this outcrop, however, nothing is to be found but the red clays which are now believed to belong to the upper part of the Coal-measure series above all the workable coals. 'These may be seen lying horizontally or dipping at a very gentle angle to the northward or north-westward at Catshill, and all down by Walsall Wood to Stubbock's Green. From under these red clays the dark coal-bearing measures then rise to the southward towards Linley and Aldridge.
It appears certain that the coals which crop about the Brown Hills, and are known to be cut off by a fault there running north-north-east and south-sonth-west from Watling Street to the canal a little east of Birch Coppice, are thrown down under Clayhanger to a depth of more than 1,000 feet (300 or 400 yards), and that they lie at that depth under all Walsall Wood, forming the bottom part of the Coal-measures from which coals are now being got at the Coppy Hall colliery at Stubbock's Green, and that were proved to exist at the Aldridge Trial pits a little north of Red House.
It seems also certain that the Clayhanger fault must continue somewhere down by Goblins Pit Wood and Shelfield, towards Coal Heath, with a downthrow to the east.
It seems also quite certain that the abrupt northern termination of the limestones of Daw End and Hay Head along a certain line, with the equally abrupt coming in of Coal-measures immediately north of that line is the result of a fault having a downthrow to the north-east, and it is very probable then that the two faults thus proved to have a similar large downthrow, are in reality one fault, forming a branch of the boundary fault. If this be so the eastern boundary fault will form two step-like eastern downthrows from the Brown Hills to Hill End, south of Aldridge, while south of that it again becomes only one downthrow, but not of so large an amount, so that it allows the Permian rocks to appear at the surface on its eastern or downthrow side, instead of bringing down the New red sandstone to the level of that surface.
The Western Boundary fault—If we begin on the south, we may say that the western boundary fault of the coal-field commences at the northern slope of Wychbury Hill. Thence to Oldswinford we have the Brick red sandstone and conglomerates on one side, and the upper Coal-measures on the other side of the fault. North of Oldswinford we get the Thick coal on the upcast side of the fault, cropping up against it and into it at an angle of 45° west of the "Grange," and on the downcast side we get a narrow band of Permian, soon overlaid by the base of the New red sandstone.
By Penn's Hill and Dennis to Audenham Bank, the beds below the Thick coal crop on the east of the fault, the Thick coal ranging up to it a little south of Brettell Lane, while the red rocks may be frequently seen at the surface just westward of the line drawn on the map.
Near Wordesley the New red sandstone dips at an angle of 20° to the west; the Permian, therefore, must here dip, at least, at as great an angle from the fault. At Bug Pool they sank through the fault down into the Thick coal below in consequence of the great overhanging ("bade," "overlie," "underlie," "inclination,") of the fault. In these pits they had 40 yards of "red rock," and got the Thick coal at 126 yards from the surface. Between Wordesley and Salters Hill. Mr. Bond sank 280 yards (840 fect) in the Permian rock at about 200 yards from its surface boundary, without passing through it into the Coal-measures. At the New Bromley Lane colliery south of the Stand Hills. Messrs. Davis have recently passed through the overhanging fault into the Coal-measures at a depth of 142 feet.
The junctions of the great faults called the Brockmoor. Corbyn's Hall, and Shut End faults with the Boundary fault (or perhaps we should say the separation of these great branches from it) appear to have little or no effect on its character. At Kingswinford the Brick red sandstone of the New red formation comes up against the fault, and we have that sandstone on the one side and the Coal-measures, with the Thick coal 140 yards (420 feet) deep, on the other. Before reaching Himley Park the boundary fault seems to split and let in between its branches a wide tract of Permian rocks, occupying the eastern half of Himley Park, all Baggeridge Woods, and great part of Penn Common.
Indications of the extension of the west branch of this fault into the New red sandstone were observed as far as the Lloyd farm, by Mr. Beckett of Wolverhampton.
The main part or true boundary fault runs as drawn in the map, with a curved line up to Sedgley Hall farm; quarries or cuttings in the Permian rocks being observed at intervals all the way on one side, and Coal-measures on the other. At the turnpike-gate west of Sedgley some small pits in a patch of Thick coal were worked formerly, and in the year 1828 a trial pit was sunk just east of Sedgley Hall farm. In this trial pit the Thick coal was found at a depth of 323 feet, dipping to the west at an angle represented as only 12°. But as a quarry in the Permian rocks may be seen just north of the farm, and the limestone ridge rises immediately on the east of it, it is clear that there must be a fault on each side of this patch of Coal-measures. Moreover the first 120 feet in this shaft was described as "red croprash rock and marl," which were in all probability Permian rocks. From these facts it is probable that the boundary fault "hades" here, at a comparatively low angle, to the west, leaving a long space of " barren ground" between the ends of the Thick coal on opposite sides of the fault (see Horizontal Sections. Sheet 24. No. 6). This is probably the general character of the boundary fault in the southern part of its course. Along the flank of the Sedgley ridge all we know of the boundary fault is that there are Silurian rocks on the high ground on one side, and Permians in the valley below.
In the Parkfield coalworks beyond, as also in the Cockshutts and Green Lanes collieries, the Coal-measures are very violently broken and contorted,[4] and a very common feature is a rapid dip of the coal measures towards the fault as they approach it.
Patches of Thick coal were found in the shafts south of the Fighting Cocks dipping at the fault. Lord Ward's agent. Mr. R. Smith, informed me, that at one spot, after the Blue flats ironstone had risen to the surface in the form of an S from a depth of 100 yards, so that one shaft passed through the same measure three times, they sank a shaft a little farther west, in which, after passing through a few yards of "Red rock," they came down to some Thick coal, dipping west at a gentle angle, which they followed for a few yards till they found it cut off by another fault, hading rapidly to the west.
At a pit sunk in the Green Lanes, Wolverhampton, they found the Brooch coal at a depth of 30 or 40 yards (90 to 120 feet), dipping west at 2 in 3 (=34°), but as they sank deeper they found the dip of the beds increasing to 2 in 1[5] (=63°). This was very close to the line of the fault. At the tunnel of the railway at Wednesfield Heath the New mine coal cropped very gently up towards the fault for several hundred yards, and was exposed in the cutting of the railway.[6] Just at the east mouth of the tunnel they met with the "Red rock," dipping westerly, and the coal as it approached it was likewise seen suddenly to dip towards the west, being much broken. The Blue flats ironstone, 160 or 170nbfeet below the New mine coal, was worked under the tunnel for nearly 100 yards beyond the end of the New mine coal, which would make the "hade" of the fault not much more than 30° from the horizon. At other places, however, between here and Wolverhampton, the fault seems from the workings to approach very nearly to a vertical. From Wolverhampton to within a mile and a half of Cannock, Permian rocks are believed to be those found below the surface on the downcast side of the fault; but at Wyrley Bank these rocks seem to be dying out, and beyond that the Brick red sandstone and conglomerate of the New red is alone seen. A split of the fault is thought to take place near the Walk Mill, one branch proceeding due north towards Stafford into the middle of the New red, while the other continues to form the boundary of the coal-field as far as Hednesford Pool, when that likewise so far dies out as to allow some of the beds of the New red sandstone to appear on the upcast side of it. The country is here so obscure that it is very difficult to say how this takes place—whether the fault becomes evanescent, or whether the beds of New red sandstone on opposite sides of it stood originally at very different levels in the formation.
The red clays of the Essington Wood brick pits are brought in apparently on this side of the coal-field, in the same way that those of Walsall Wood are brought in on the other. A split of the boundary fault as it ranges south seems to take place about Cheslyn Hey, the upper red Coal-measures making their appearance at the surface between the branch and the main boundary fault. The dip on this western side being to north-west, the black coal-bearing measures rise out to the southward towards the Old Mitre, just as they rise out towards Daw End on the eastern side of the coal-field, the downthrow of the branch fault decreasing in each case towards the south. It is possible that the branch on the western side, which we may call the Old Mitre fault, which is known to have a downthrow of 65 yards to the west thereabouts, runs on to the south till it is cut off either by the New Invention fault, or even till it reaches the extension of the Great Bentley fault.
Position and Lie of the Red rocks surrounding the coal-field.— We will now briefly recapitulate what we know of the Permian rocks surrounding the coal-field, and then describe the position of the beds of the New red sandstone around it.:
Permian.—The Permian rocks in the narrow belt which runs S.S.W. from Cheslyn Hey towards Wolverhampton are covered towards the west by beds of conglomerate belonging to the New red sandstone, occasionally seen in situ; but still farther west. Professor Ramsay informs me that brown speckled sandstone (Permian) is seen at one or two places, especially in an old quarry a little to the N.E. of Bushbury Hill, and that the way in which these rocks appear involves the necessity of their being brought to the surface by faults having upthrows to the west, as drawn in the latter editions of the map and in Mr. Hull's Section. No. 45.)
Pale wine-coloured and nearly white sandstones, often highly calcareous, were exposed in the cuttings of the railways at Wolverhampton, dipping sometimes at an angle of 5° or 6° to the west. These were also believed to be Permian sandstones. Just west of the road, however, near the windmill in Stafford-street, good brick red sandstone, certainly part of the New red, is well shown in a quarry, and appears to be quite horizontal. The new shaft for the waterworks at Goldthorn Hill is sunk entirely in mottled calcareous sandstones and marls of the Permian series. These were said to dip westerly across the shaft at an angle sometimes of 30° (Vertical Sections, Sheet 26, No. 50). On the crest of the hill to the westward are some gravel pits opened in the pebble beds of the New red sandstone, which likewise appear to have a slight westerly dip.
Indications of Permian beds on one side of the boundary and a gravel ridge (pebble beds of the New red) on the other are found from Goldthorn Hill to Penn Common. Permian marls and sandstones may be seen in the lower part of the brook south-east of the Lloyd House, and typical New red sandstone at the mill by the Wood-houses. Near Gospel End, the Permian beds, consisting of alternations of reddish and pale brown sandstones with red marls, and a band of slightly calcareous conglomerate, may be seen in some road cuttings. These Permian beds have everywhere hereabouts a dip of 5° or 10° to the west-north-west. A large mass of calcareous conglomerate, similar to that of Barnford Hill on the east of the coal-field, was found and mapped by Mr. Hull in Baggeridge Wood. At Hawkeswell Rough, north of Himley Park, good New red sandstone is seen apparently horizontal, while on higher ground to the eastward are two quarries of pale Permian sandstone, one of which dips north-east and the other south-east at 10°. A fault, therefore, must here separate the two formations. This is believed to extend northwards into the New red sandstone and southwards across Himley Park to the boundary fault. Just behind Himley Hall the conglomerates of the New red sandstone are well shown in a large cliff dipping north at 10°. Pale slightly calcareous sandstones may be seen about the Streights dipping north-west at 5°.
A narrow belt of Permian rocks just peeps out between the New red sandstone and the boundary fault between Kingswinford and Oldswinford. They consist principally of pale red calcareous sandstone and red marls. At Audenham Bank a concretionary mass of compact pale grey limestone, with a smooth conchoidal fracture, was exposed in the bank of the road lying in some red marl. It did not seem to extend far, however. Professor Ramsay informs me, that in a new road cutting near Dennis. Permian sandstones and marls containing slight traces of the trappean breccia may now be seen dipping west at 10° or 15°.
The Permian district round the south end of the coal-field is the largest and most important one of the neighbourhood, and worthy of a little more detailed description. When the country was first surveyed, no doubt was entertained that the Clent Hills consisted of trap rock, and that the angular fragments seen at the surface and in the small quarries were the local débris of the solid rock below. Professor Ramsay, who spent a day with me there in 1849, concurred in these views, which are those published by Sir R. Murchison in his "Silurian System." On examining the Lickey Hills, however, it was soon perceived that the angular trap débris there rested on red sandstones, which had not then been separated from the New red sandstone formation. This trappean débris, therefore, was at first taken by myself for local drift, derived from the Clent Hills. In some places, however, it was seen apparently to pass under beds of the New red sandstone age, and therefore supposed there might have been a drift of it during the formation of that rock, and another of more recent epoch, deriving its materials either from the breccias of the New red, or directly from the Clent Hills, or partly from one and partly from the other. While examining some of these angular trap breccias. I was often led to entertain doubts as to their being really any trap in situ in the Clent Hills, but the trappean prestige was so strongly upon them that I did not venture to disturb it. The district indeed, though frequently traversed, was not then surveyed, as the " red rock" country was left till after the Coal-measures and older rocks were completed. Before even the coal-field was finished. I was called away (in 1850) to Ireland to assume the local direction of the survey there in consequence of my predecessor Professor Oldham's departure for India; and it was not till the year 1852 that I was enabled to return for a short time to complete my work sufficiently to allow of its publication. In the meantime Professor Ramsay and Mr. Hull had examined and made themselves masters of the Permian rocks, as shown in the North of Staffordshire; and Mr. Hull examined and partially surveyed the Permians round the South Staffordshire coal-field. Mr. Hull satisfied himself that the angular trappean breccia belonged to the Permian formation, and was a characteristic portion of it. In the spring of 1852 Professor Ramsay joined me in the district, when I had completed the examination of the coal-field; and we were soon aware that a more detailed and accurate survey of the Permian rocks round the south end of the coal-field was necessary. As I was compelled to go to London in order to make arrangements for the publication of this Memoir and free myself for what had become my more legitimate duties in Ireland. Professor Ramsay very kindly consented to devote some of his own time to the examination of this district; and the following are the results of this examination as he has provided me with them.[7]
The Clent Hills and Wychbury Hill (formerly considered to be trap, and coloured as such in my own working maps,) consist altogether, as far as their higher portions are concerned, of the angular trappean breccia, with no appearance of any trap in situ at all, "the fragments being principally composed of greenstone, with a little sandstone and a porcelanic looking slaty rock like some of those west of the Stiperstones." The beds are rudely stratified, and appear to dip south or south-south-west at an angle of about 5°. This angular trappean breccia may be traced continuously from from Hagley Park to Broomsgrove Lickey, forming the uppermost of the Permian beds, having always a southerly dip, and passing in that direction under the " pebble beds" or conglomerates of the New red sandstone. The breccia is frequently a very deep red, the fragments being cemented together as it were by a red marly substance. When well exposed it is seen to pass insensibly at its base into red marls, the fragments getting smaller and finally disappearing.
Underneath this are red sandstones and marls, and then a band of highly calcareous sandstone comes in, showing itself under Square coppice at the Lickey, of the limeworks of Newtown, near Hunnington, near St. Kenelm's chapel, and west of the parsonage in Hagley Park. Near the latter spot the pebble beds of the New red appear to overlap the trap) breccia and approach the calcareous band,[8] running up nearly to the obelisk. They are then cut off by a fault which has been recently exposed in a new gravel pit, and the trappean breccia again comes out to form Wychbury Hill. A similar fault, bringing down the gravel beds to abut against the trappean breccia, is believed to terminate it at the Lickey Hill, just north of "the High House" (see Map). The lower beds of the formation, consisting of red and brown sandstones and marls, with one or two calcareous bands, spread over the country from Hagley Wood to Frankley, Kitwell, and the Lappal tunnel, the beds having, doubtless, a general slight inclination to the southward, with several minor flexures. Another patch of the trappean breccia caps the hill on which the well-known trees called Frankley Beeches stand.
From Frankley the dip appears to be south-south-east, and this inclination brings in the trappean breccia again in that direction, dipping in the lane north of Merrit brook at 20° to the south-south-east. Here all the Permian rocks are cut off to the eastward by a fault, believed to be an extension of the eastern boundary fault; and New red sandstone occupies the triangular district between Shenley Court and Weoley Castle. Brick red sandstone comes in south-east of the last-named trappean breccia, resting on it at one place apparently in a horizontal position, but in another appearing to dip from it at an angle of 15°. This sandstone, together with the Permian and other rocks between it and the Lickey, are all believed to be cut off by a fault running north-east and south-west, which will be described presently. From Frankley the Permian rocks extend northwards to the Lappal tunnel, and then, after being apparently interrupted by the Coal-measure tract running down to the Stonehouse, they occupy a broad band of country, extending northwards, between Oldbury and Smethwick, and thence by Great Barr to the ground between Barr Beacon and Hey Head. This Permian tract has already been described (pp. 11, 12, 177, and 178), when speaking of the Coal-measures as coal is worked through part of it.
New red sandstone.— We have now very briefly to examine the position of the rocks forming the New red sandstone formation. The northern part of Cannock Chase consists of red sandstones and pebble beds belonging to the middle and lower portions of the New red. These rocks must dip very gently to the north-north-east, in which direction they pass under the upper red marls on the north side of the rivers Sow and Trent. Similar beds on the east side of the coal-field between Lichfield and Rugeley, having @ similar dip, likewise pass under the red marls north of the river Trent. These marls, partly by the northerly dip of their beds, partly by the rise of the ground in that direction, become eventually capped by two large patches of Lias, the one occupying Bagot's Park and part of Needwood Forest, the other spreading round Christchurch on Needwood (see Map. Sheet 72, south-east). The sandstones under these marls rise to the westward algo, and crop on the high ground between Ingestre and Stafford; but the bottom parts of the red marls are suddenly brought in again by a downcast fault, which is believed to be an extension of the branch that comes from the western boundary fault near Cannock. In consequence of this depression of the beds, the red marls spread themselves over all the country from Stafford to Penkridge and Brewood as far south as Wrottesley Park, and even to the south of that another patch of them is thought to be brought in by a fault, so as to cap the high ground between the Wergs and Nurton. From this point the middle and lower parts of the New red sandstone are seen to stretch uninterruptedly to the southward, till they are again covered by the red marls of Worcestershire a little south of Bellbroughton.
Between Cannock and Wombourne the general dip of those beds must be to the north-west, both from their passing under the red marls in that direction and from their allowing the Permians to rise from beneath them on the south-east.
From Wombourne to the neighbourhood of Stourbridge they probably scarcely deviate from horizontality, except where they rise to the eastward to allow the Permian beds to appear at the surface, or are tilted slightly on approaching the boundary fault of the coal-field. South of Hagley and Clent the general inclination of the New red must be to the southward, the pebble beds rising on to the flanks of the Clent Hills,[9] and the red marls setting in south of Bellbroughton and at Chaddesley Corbett, and Elmsley Lovett.[10] Between these places the red marls are underlaid by a white sandstone exactly similar to that under the marls near Albrighton and about Codsall, Brewood, Penkridge, and Rugeley. Plants were found in it by Professor Ramsay near Bellbroughton similar to those described by Sir R. I. Murchison and Mr. Strickland in their paper in the 5th vol. of the Geological Transactions.
These Worcestershire marls have a general south-easterly dip, which brings in the Lias east of Hanbury. My colleague. Mr. Howell, partly by himself and partly in conjunction with Professor Ramsay, had mapped the red marls continuously from the Lias of Needwood Forest, by Lichfield. Tamworth, and Birmingham, to Droitwich; and Professor Ramsay informs me that this Lias near Hanbury is precisely similar in mineral character to that of the outliers of Needwood in Staffordshire, consisting of " pale clay below, with interstratified beds of pale bluish argillaceous limestone, covered by brownish white, very thin bedded, micaceous sandstone, containing casts of small bivalve shells." 'The extension of this Lias to the eastward is cut off by an upcast fault running north-west, in which direction the red marls are themselves cut off to the east, and red sandstone brought up against them, probably by the same fault running generally north in a slightly curved line. It is not improbable that this fault runs much farther north, and is in some way connected with the western boundary fault of the coal-field. If so, we have strong presumptive evidence for a fault, running generally north and south with a downthrow to the west for upwards of 40 miles, or from the latitude of Stone to that of Droitwich (see Map, Sheets 72, south-west; 62, north-west and south-west; and 54, north-west).
The New red sandstone between Bromsgrove and the Lickey Hill has a general dip to the south-west and south, and the white sandstone comes in around Bromsgrove, passing under the marls to the southward of it. This white sandstone likewise contains fossil plants at Hill Top near Bromsgrove. It appears to pass laterally as well as downwards, into red sandstone. If we start from the natural boundary of the red marl, south of Bromsgrove, and walk across the country to the pebble beds of the Lickey Hill, a distance of about four miles, we should find that every exposed piece of rock showed a dip to the southward or south-westward, sometimes at an angle even of 10°. Whatever allowance we make, therefore, for undulations of the beds, we must necessarily suppose a very considerable thickness to interpose between the bottom of the red marls and the bottom of the pebble beds. If, however, we pass on to the east side of the Lickey quartz ridge, we shall find the natural boundary of the red marls coming up within a mile of the older rocks, and near Kendal end, within 100 or 200 yards of them. As the beds do not seem to have any greater amount of dip on the east of the quartz ridge than they have on the south-west, we must either suppose the whole of the red sandstone to have thinned out here, and the red marls to overlap nearly the whole of the lower beds, or a very considerable downthrow fault to traverse the east side of the quartz ridge. Moreover, the thick pebble beds lying on the south-west flank of the quartz ridge cannot be traced round its southern extremity, nor seen anywhere to the eastward. It is probable, therefore, that they are concealed under the other beds there by means of such a downcast fault. Several other faults have been found affecting the margin of the red marls, as may be seen in the map.
We have already mentioned a south-west and north-east fault, supposed to start from the sides of the quartz ridge near the coalmeasures, and run to the north-east. This has a downthrow to the south-east, and brings down the New red sandstone level with the ends of the Silurian. Coal-measures and Permain beds, between the Colmers and Mason's Lodge. Farther to the north-east it brings the red marl down against the lower part of the New red, namely, the brick-red sandstone, and it then runs off to the north-east through Birmingham, up nearly to Sutton Coldfield, bringing the red marls down against various parts of the New red sandstone. From the eastward of Sutton Coldfield the red marls stretch to the northward uninterruptedly to those before mentioned, north of the Trent, between Barton-under-Needwood and Abbott's Bromley.
The New red sandstone included between this marl boundary and the coal-field consists of brick-red sandstones near Birmingham, part of the upper Bunter sandstone, lying either horizontally, or dipping very slightly to the east, and allowing of the outcrop of a thickish band of pebble beds that usually form the boundary of the New red towards the Permian district. These pebble beds may be traced, more or less continuously, from the Lightwoods near Harborne to Barr Beacon. They apparently extend eastward a good way about Sutton Park, but they approach the boundary of the coal-field again about the Brown Hills, and coming against the fault are cut off by it, dipping north under the upper part of the New red, and only just rising up and re-appearing at the surface on the high ground west of Brereton, from which place they join on to those of the north part of Cannock Chase. Between Lichfield and Rugeley we have only the upper parts of the red sandstone, those lying just below the red marls as before described; so that if the ground were a little higher, the tops of the hills would all be capped by the red marl, as is the hill at the Old Lodge.
- ↑ It is a curious instance of the frequent want of the commonest knowledge in this district, that an intelligent man who acted often as a "ground bailiff" in the neighbourhood, his father and brother being both of that profession, was yet not aware that it was impossible to find coal beneath shale containing Silurian fossils.
- ↑ A dotted line was drawn on the map to call attention to the probable connexion between these two places. This connexion subsequent workings near Spon Lane have proved not to exist on the Thick coal level all the way, at all events not to run along the exact line drawn in the map, though it may run a little farther east of it.
- ↑ It might give a more natural aspect to the facts, perhaps, if we supposed another branch to spring from the boundary fault between Ray Hall and Small's farm, and run a little north of West Bromwich old church to the fault that cuts off the Thick coal crop of the Hall End colliery. This line of fault would blend with that which certainly runs under the Cross Guns more easily than the one engraved on the nap south of Church Vale, or, perhaps, the two together might form steps letting down the Thick coal under Virgin's End, &c.
- ↑ Not far from the Fighting Cocks a pit was sunk formerly where Mr. Pugh's house stands, in which pit the New mine coal, 6 feet thick, took 30 yards (90 feet) of perpendicular depth to traverse the width of the shaft, 7 feet. It dipped, therefore, at an angle of 81°.
- ↑ That is, in a seven-foot shaft, after passing through one measure on the crop side of the pit, they sank 14 feet deep before they left it on the dip side of the shaft.
- ↑ This is stated from my own personal recollection of the cutting at the time of the formation of the Grand Junction Railway.
- ↑ I have entered on this personal detail in order that I may not seem to be taking more credit than I deserve, and also to strengthen my statements by the authority of Professor Ramsay.
- ↑ Unless this be the effect of a fault, a part perhaps of the boundary fault of the coal-field.
- ↑ The quartzose gravel or pebble beds of the New red sandstone about Clent and Calcot Hill rest directly on or against the angular trappean breccia of the Permian formation. Notwithstanding the incoherent and easily transported character of the materials of the two formations, their boundary is wonderfully distinct, so much so that it can be traced across ploughed fields merely by the nature of the pebbles and fragments lying on the surface, so little have these been mingled either during the deposition of the New red or at any subsequent period.
- ↑ From this to the end of the chapter is an account of the work done by Professor Ramsay, assisted by Mr. Howell.