DIGGING OUT A BOULDER. .153 



DIGGING OUT A BOULDEE. 



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 anji}hing certain aboiit it." lu 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 gi-avel, which are 

 Been at certain points to be overlaid by a stiff, clayey mass, full of 

 stones of aU sorts and sizes, to which the name of the " Great 

 Chalky Boulder Clay" has been assigned, from the number of frag- 

 ments 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 a 

 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 Chamwood Forest, as we might expect from its immediate 

 proximity. Of rocks foreign to England no authenticated instance has 

 ever occurred. 



Of the Chamwood Eocks 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 sui-face in the vicinity of 

 the famous quarries. The stone is a hornblendic gi-anite, finely crystal- 

 lised, 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 

 some very fine blocks. 



Some of these boulders have attained to the dignity of a mention in 

 the pages of the historian, and among these is the mass whose disinter- 

 ment I am about to describe. 



It is situated in a field 2| 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 Ehaetic Beds and Lower Lias, which 

 forms the eastern boundary of the Soar YaUey. The boulder clay in 

 which it is embedded rests on the Lower Lias, the mid-glacial deposits 

 being absent. Mountsorrel bears north-west, and is on the west side of 

 the Soar Valley, which the boulder has consequently crossed. The spot 

 where it now Hes is about 260ft. above the level of the sea. 



In Nichols' Histoiy of Leicestershire, (Vol. JU., p. 981,) this stone 

 is referred to by the Eev. Mr. Woodcock, who says that there is a tradi- 

 tion that a house, or cell, or nunnery, having some underground connec- 

 tion with the Abbey of St. Mary de Pratis, in full view of which it would 

 stand, was once situated here. The block was called " Hellstone," or 

 " Holstone," and the field "Hoston Field," a word which seems to be a 



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