312 T. Mellard Reade — Glacial Geology. 



The Boiilder-clay is usually of a brown colour, sometimes unctuous, 

 and contains boulders and fragments of Northern rocks from the 

 maximum of over 20 tons down to the finest gravel. The boulders 

 are to the extent of fully 50 per cent, either planed or striated or 

 both, and sometimes on several faces. They are often considerably 

 rounded and the finer gravel to be obtained by washing the clay is 

 extremely waterworn. The sand, if separated from its clayey 

 matrix, is much rounded, some of the grains being extremely 

 polished. 



The proportion of sand in the clay is much greater than would 

 at first be thought, varying from 20 to 60 per cent. There is no 

 geological difference between the Sands and the Boulder-clays, 

 gradations from the one to the other can be met with though ofteu 

 they come together in sharp juxtaposition. If we trace these drift 

 deposits up the valleys from the sea to the source of the rivers 

 flowing in them, we find that the nature of the matrix of the drift 

 lying in them is largely dependent upon the nature of the rocks the 

 rivers traverse,' that is to saj^ the sandy and gravelly drift increases 

 when the rivers above them flow through sandstones and rocky 

 ground as in the Dee above Chester, and the Mersey and Irwell in 

 the neighbourhood of Manchester, while the rivers flowing over the 

 New Ked Marl have brought down an unctuous clay like that 

 deposited by the Weaver in the Buried Valley of the Mersey at 

 Widnes. Thus, while the contained stones have come from the 

 northward, with the possible exception of some sandstones and 

 gypsum of the New Red Marl, the matrix consisting of clay and 

 sand has to the larger extent come down the river valleys. 



If we extend our observations further south into Shropshire we 

 find a still greater development of sands. The drift by the Severn 

 at Shrewsbury is nearly all red sand, the waterwashed debris of the 

 New Eed rocks. The erratics are still plentifully strewed about the 

 county, and the well-known Eskdale granite and the grey granite 

 of the south of Scotland, together with the andesitic rocks and 

 volcanic ashes from the English Lake district are distinguishable. 

 It is also a fact worth noting that on the plain of New Red Marl in 

 Cheshire the drift sands and gravels are more developed than the 

 Boulder-clay ; often they lie directly upon the marl without the 

 intervention of any Boulder-clay. I have observed this also in 

 Shropshire. 



High-Level Sands and Gravels. 



At Moel Tryfaen, Carnarvonshire ; at several places in Flintshire 

 (Moel-y-Crio among them) ; between Minera and Llangollen, Denbigh- 

 shire ; at Gloppa, near Oswestry ; at the Setter's Dog, near Maccles- 

 field, and the Three-Rock Mountain, near Dublin, sands and gravels 

 are found varying from about 1000 to 1400 feet above the sea-level. 

 These sands and gravels contain shells of mollusca, speaking generally, 

 of a similar fades to those fragments found in the Low-level Boulder- 

 clay and sands. More perfect specimens have been found at these 

 high levels, especially at Gloppa, by Mr. Nicholson, F.G.S., than 

 ' Quart. Joum. Geol. Soc. vol. xxxix. pp. 83-132. 



