316 T. Mellard Reade — Glacial Geology. 



northern rocks along with it. A short Iceberg period must have 

 jireceded the final development of the Ice-sheet, even on this theory, 

 and the products of this interval might get ploughed up and mixed 

 with the products of the Ice-sheet. But what has become of the 

 Pre-glacial deposits ? I have examined most artificial exposures 

 in Lancashire and Cheshire calculated to throw light upon the 

 subject, but nothing in the form of a Pre-glacial deposit have I ever 

 seen. The Alexandra Docks at Liverpool and the Docks at Garston 

 gave grand opportunities for inspecting the rocky floor below tide 

 level, the Mersey Tunnel also, in a lesser degree, but everywhere 

 the glacial deposits rest directly on the bed-rock or the debris of 

 the bed-rock. Borings at Widnes and well and shaft sinkings at 

 various places in the Mersey Valley, all below the level of the sea, 

 tell the same stoiy. So far as we know, and I have seen nothing 

 recorded to the contrary, the glacial deposits, with local variations, 

 are the same from the top to the bottom of the series. The " Gully 

 Gravels" lying in depressions down to 160 feet below the sea level 

 are glacial, as shown by the rocks from which they have been 

 derived being the same as those in the Boulder-clay. If, as is con- 

 tended, the Drift of Lancashire and Cheshire is ploughed-up Irish- 

 Sea bottom, it is very remarkable that it possesses such homologous 

 characteristics throughout, and that the Pre-glacial deposits have 

 been so thoroughly mixed with the materials brought by the land- 

 ice that there is no distinguishable difference from the top to the 

 bottom of the series. Not only are Pre-glacial deposits not to be 

 found in situ, but not a scrap or shred of anything of the sort have 

 I ever found embedded in or associated with the Boulder-clay. 



Areal Distrihution of Erratics. 



Not only are the rocky materials contained in the Drift not 

 arranged in any discoverable vertical order, but well recognized 

 types of rock have a wide areal distribution. All over Lancashire, 

 Cheshire, and Shropshire, Scotch and Eskdale gi-anites are to be 

 found in large boulders now scattered over the surface, while smaller 

 boulders and pebbles of the same rocks are to be seen in the Drift 

 itself. East and west they extend also from the Pennine Chain 

 across Lancashire and Cheshire and along the coast of Wales to 

 beyond Moel Tryfaen, in Carnarvonshire. 



If all these boulders have been conveyed to these points by an ice- 

 sheet, some reasonable explanation of how it was done ought to 

 be given. 



This hypothetical ice-sheet is supposed to have originated in 

 Scotland, and to have been reinforced by glaciers from the north- 

 west of England and the north-east of Ireland. Its course was 

 over the bed of the Irish Sea to Liverpool Bay, at which place it 

 divided into two lobes, one of which flowed onwards over Cheshire 

 and Shropshire, and the other flowing westward, skirted the coast 

 of Wales. Taking Criflfel as the origin of the Scotch granite, it 

 would form the apex of a triangular area over which this granite 

 has been distributed, having a base — measuring east and west along 

 the coast of Wales— as long as its sides. 



