A HISTORY OF LANCASHIRE
On the other hand, the intervening shales contain brackish and marine forms of life more nearly related to those of the Yoredale shales and Carboniferous limestone below. A species of Lingula is most common, but species of Productidæ, Streptorhynchus, Spirifera, Aviculopecten, Modiola, Posidoniella, and Goniatites also occur. Fish remains are rare.
The Millstone Grit Series is separated into four divisions:—
First Grit, or Rough Rock.
Second Grit, or Haslingden Flags.
Third Grit.
Fourth Grit, or Kinder Scout Rock.
| Rough Rock. | One or, more usually, two beds of massive coarse grit, separated by a twelve to eighteen inch seam of coal called the 'Feather Edge' Mine. |
| Shales | Usually thin and at times absent. In the Rossendale area from 30 to 100 feet thick. |
| Second Grit, or Haslingden Flags. | Fine-grained hard grey sandstone forming three beds in the Rossendale district. |
| Shales | A shale series containing a thin coal at the base, and a workable seam at Mossley and Mottram, in Cheshire. |
| Third Grit | Fine grits and flagstones, the lower beds being especially thick and coarse. |
| Shales | Shales with two thin coals near the base. |
| Fourth Grit, or Kinder Scout Rock | Massive coarse sandstone grits, with conglomerates and shales. |
It must not be supposed that the sequence of beds given here can always be determined. Many of the grits are much current-bedded, whilst their thickness is constantly changing, and important members are in some places absent. The Kinder Scout and Rough Rocks are the most stable members of the series, the Second and Third Grits being more lenticular in form, so that their thickness, even in adjoining districts, may vary extremely.
Kinder Scout Rock.—This rock consists of two or more beds of grit, varying in their character from ordinary sandstones into conglomerates, the pebbles consisting of quartz which is mainly milky in colour, the glassy form being less constant. Rotten felspar and flakes of mica are also abundant, so that the coarser grits have a granite-like appearance. The extensive Millstone Grit capping of the Anglezark, Wheelton, and Withnell Moors and Bromley Pastures is formed of this grit.
To the north of Anglezark Moor is a long elevated ridge of Kinder Scout Rock, passing from Holster Hill two miles north of Hoghton Tower in a direction E 38° N. by Mellor, Whalley Nab, and Wiswell Moor to Nick of Pendle. Along the foot of Pendle and at Newchurch-in-Pendle outcrops are numerous. In the neighbourhood of Cocker Hill the grit consists of two beds of coarse sandstone separated by about 125 feet of shale. The total thickness has been estimated by Prof. Hull as between 750 and 800 feet. It forms a well-marked feature in the neighbourhood of Foulridge, north of Colne.
The Kinder Scout Grit is well seen to the east of Oldham cropping out in the valley of the Tame from Warmton Wood to Harrop Edge, and stretching on into Cheshire and Yorkshire. On the Yorkshire side of the boundary at Chew Brook and Greenfield the grit rises into bold, majestic cliffs. The thickness is here estimated at 500 feet, but this is increased at Saddleworth owing to the greater development of one of the beds of shale.
A fine section is exposed along the Mottram and Staleybridge road at Roe Cross, where the total thickness has increased to about 1,000 feet.
Shales.—The shales seen on the flanks of Winter Hill are supposed by Prof. Hull to lie above the Kinder Scout Rock and below the Third Grit. They attain a thickness of 350 to 400 feet. In the river Darwen below Malmesbury Mill they show a thickness of 625 feet, and the bottom is not seen. They have been traced to Whalley, where they occur in the bed of the river Calder and also between Wiswell Moor and Sabden.
Between Rough Lea Water and the road from Colne to Foulridge exposures are difficult to find, but numerous sections occur south of the canal reservoir.
In ironstone nodules from the shales, and in the shales themselves, have been found Goniatites, Posidoniella lavis, and fish remains, together with Calamites.
Two thin coal seams occur at the base of the shales in Dean Brook at the northern end of Rivington Hill, and also at Grange Brook near Belmont.
At Pule Hill on the eastern side the shales vary from 100 to 300 feet in thickness. They show a tendency in both localities to become sandy or flaggy.
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