Midland Naturalist/Volume 01/Digging Out a Boulder
Digging Out a Boulder.
By W. J. Harrison, F.G.S.
A few days since an eminent Geologist remarked to me—"Twenty years ago I thought I knew all about the drift; now I am doubtful if I know anything certain about it." In fact, the more those surface deposits which we assign to the glacial period are studied, the more difficult does the problem of their precise origin become. In Leicestershire we find the oldest glacial deposits to be beds of sand and gravel, which are seen at certain points to he overlaid by a stiff, clayey mass, full of stones of all sorts and sizes, to which the name of the "Great Chalky Boulder Clay" has been assigned, from the number of fragments of chalk which it, contains. This arrangement holds good elsewhere, but both on the east coast, (Lincolnshire, &c.,) and the west coast, (Lancashire, &c.,) the sandy, gravelly deposits are underlain by clayey deposit, or Lower Boulder Clay, which is absent in Leicestershire.
In the Upper Boulder Clay of this county there are many fine masses or erratic blocks, some of which are referrible to the Mountain Limestone, others to the Millstone Grit or carboniferous sandstones, still others to the Lower Oolite, but the finest masses are decidedly those from Charnwood Forest, as we might expect from its immediate proximity. Of rocks foreign to England no authenticated instance has ever occurred.
Of the Charnwood Rocks none are more readily recognisable than those of Mountsorrel, under which name I include the entire igneous mass which covers about one square mile of surface in the vicinity of the famous quarries. The stone is a hornblendic granite, finely crystallised, and of a pink or grey hue according to the tint of the felspar. Erratic masses of this rock occur at intervals along a definite line on the east side of the Soar Valley, a line which is marked by the occurrence of soma very fine blocks.
Some of these boulders have attained to the dignity of as mention in the pages of the historian, and among these is the mass whose disinterment I am about to describe.
It is situated in a field 2¾ miles north-east of Leicester, and on the north side of the road from Humberstone to Thurmaston. Here it lies nearly on the top of the low ridge of Rhactic Beds and Lower Lias, which forms the eastern boundary of the Soar Valley. The boulder clay in which it is embedded rests on the Lower Liss, the mid-glacial deposits being absent. Mountsorrel hears north-west, and is on the west side of the Soar Valley, which the boulder has consequently crossed. The spot where it now lies is about 260ft. above the level of the sea.
In Nichels' History of Leicestershire, (Vol. III., p. 981,) this stone is referred to by the Rev. Mr. Woodcock, who says that there is a tradition that a house, or cell, or nunnery, having some underground connection with the Abbey of St. Mary de Pratis, in full view of which it would stand, was ounce situated here. The block was called "Hellstone," or "Holstone," and the field "Hoston Field," a word which seems to be a corruption of "Holystone." The boulder lies fifty yards within the field, not far from a hedge. Before being uncovered its visible mass was insignificant, being lichen-covered and rising only some seven or eight inches above the grass, with an area of 2ft. by 3ft., but that it extended under the turf for some distance was evident from the dryness of the surrounding patch in winter, and the burnt appearance of the grass in summer.
Nichols also tells us that this stone "seems to confirm the generally received opinion of Naturalists concerning the growth[1] of these bodies; for, notwithstanding great pains have been taken by a late proprietor of the land to keep it below the surface, it defeats his efforts, and rises gradually, though not insensibly." The Holstone is nearly three miles distant from the site of "St. John's Stone," another fine mass of Mountsorrel granite, which formerly stood in a hollow in a field near Leicester Abbey. A line joining these two masses was said to point to the rising place of the sun on Midsummer-day. It would bear two or three degrees north of east.
The occupier of the field—Mr. Kirby. of Humberstone—who is a member of the Leicester Literary and Philosophical Society, kindly undertook to have the stone uncovered, and invited a party of gentlemen interested in Geological and Archæological pursuits to view its bared proportions. On arriving on the ground on the afternoon of May 2nd, I found that a trench had been dug completely round the boulder. It was now seen to be a pentagonal mass, the sides measuring 7ft., 5ft., 6ft., 4ft, and 5½ft. respectively. Its height varied from 4ft. 9in. to 3ft. 6in. Now the average specific gravity of the Mountsorrel granite is 2.659, and, consequently, each cubic foot weighs 166.19 pounds. Taking the contents of the boulder at 200 cubic feet, we find its weight to be in round numbers fifteen tons. The matrix in which it was embedded was boulder clay of the ordinary description, rather sandy in the upper part, and full of rounded quartzite and grit pebbles from three to six inches in diameter, with broken liassic fossils, also pieces of mountain limestone, millstone grit, &c. The sides of the boulder are clean and sharply defined, evidently traversed by master-joints. No striations were visible, but they may possibly exist on the under-surface. Its top is worn into rounded hummocks, just as the summits of the syenite hills of Charnwood now weather. I have, indeed, little doubt that this mass formed a part of the then summit of Mountsorrel, when a glacier advancing southwards tore it from its home, carried it over a depression in the Soar Valley of more than 109ft., and finally dropped it at a point six miles distant from its native mass.
It would be very desirable, if possible, to remove the "Holstone" to the grounds of the Leicester Town Museum, where it would be secure from destruction, and where its ponderous proportions would form an object well fitted to attract the attention of visitors, and to awaken a desire in their minds to study the science of Geology.[2]
Many thanks are due to Mr. Kirby for his energy in the matter, and for the hospitable manner in which be entertained the party who came to inspect his "little stranger."
- ↑ The apparent growth of boulders is thus referred to in the report of the British Association Boulder Committee. "It should be mentioned here that boulders probably 'work up' to the surface. This is due, no doubt, to denudation which is taking place. In a field on Red Hill Farm, between Stafford and Stone, is one of the largest boulders of the district. This boulder was not noticed till some twenty years ago, when it was found to obstruct the plough, although still some depth underground. The obstruction became more and more serious each year and, in consequence of this impediment, the field was turned from an arable to a grazing one. At this time the boulder rises about 1ft. above the level of the field. The part exposed measures 6ft. by about 5ft., and evidently extends under the turf for a much greater distance."—Report 1873, p. 193.—Eds, M. N.
- ↑ In the event the stone was not removed; see Humberstone and Hamilton which says
The stone is located at 52°39′29″N 1°04′44″W / 52.657951°N 1.078767°W (Wikisource contributor note)The "Humber stone" is a granite monolith of unknown (perhaps glacial) origin that lies in a field in Hamilton. Until 1750 it had been fully exposed, but was then truncated and the remainder buried by a farmer. In the 1980s it was partially uncovered and made accessible to the public. It was then fenced in when the Leicester north ring road was built and had a sign erected at the site, describing the stone's history.
This work was published before January 1, 1930, and is in the public domain worldwide because the author died at least 100 years ago.
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