TRANSACTIONS OF SECTION C. 635 



thicker towards its axis than at its edges, and at the north than at its southern 

 terminus, and that it was reinforced by smaller tributary ice-streams from both 

 England and Ireland. It may be compared with the glacier of the Hudson River 

 VaUey in New York, each having a maximum thickness of something more than 

 8,000 feet. The erosive power of the ice-sheet was found to be extremely slight 

 at its edge, but more powerful farther north, where its action was continued for a 

 longer period. Towards its edge its ftmction was to fill up inequalities rather than 

 to level them down. It was held that most glacial lakes are due to an irregular 

 dumping of drift, rather than to any scooping action ; observations in England and 

 in Switzerland coinciding with those in America to confirm this conclusion. 

 Numerous facts on both sides of the Atlantic indicate that the upper portion of 

 the ice-sheet may move in a different direction from its lower portion. It was also 

 shown that a glacier in its advance had the power of raising stones from the 

 bottom to the top of the ice, a fact due to the retardation by friction of its lower 

 layers. The author had observed the gradual upward passage of sand and stones 

 in the Grindelwald glacier, and he applied the same explanation to the broken 

 shells and flint raised from the bed of the Irish Sea to the top of Moel Tryfan, to 

 Macclesfield, and to the Dublin Mountains, The occurrence of stratified deposits 

 in connection with undoubted moraines was shown to be a common phenomenon, 

 and instances of stratified moraines in Switzerland, Italy, America, and Wales 

 were given. The stratification is due to waters derived from the melting ice, and 

 is not proof of submergence. 



It was held that, notwithstanding a general opinion to the contrary, there is 

 no evidence in Great Britain of any marine submergence greater than about 

 450 feet. It was expected that an ice-sheet advancing across a sea should deposit 

 shell-fragments in its terminal moraine. 



The broad principle was enunciated that, wherever in Great Britain marine 

 shells occur in glacial deposits at high levels, it can be proved, both by striae and 

 the transport of erratics, that the ice advanced on to the land from out of the 

 sea. The shells on Three Rock Mountain, near Dublin, and in North Wales and 

 Macclesfield, all from the Irish Sea ; the shells in Cumberland, transported from 

 Solway Firth ; those on the coast of Northumberland, brought out of the North 

 Sea ; those at Airdree, in Scotland, carried eastward from the bottom of the 

 Clyde ; and those in Caithness, from Moray Firth — were among examples adduced 

 in proof of this principle. The improbability of a great submergence not leaving 

 corresponding deposits in other parts of England was dwelt upon. 



It was also held that there was insuflicient evidence of more than one advance 

 in the ice-sheet, although halts occurred in its retreat. The idea of successive 

 elevations and submergences with advances and retreats of the ice was disputed, 

 and the author held that much of the supposed interglacial drift was due to sub- 

 glacial water from the melting ice. 



The last portion of the paper discussed the distribution of boulders, gravels, 

 and clays south of the glacial area. Much the greater part of England was 

 believed to have been not covered by land-ice. The di-ift deposits in this area were 

 shown to be the result in part of great freshwater streams issuing Irom the melting 

 ice-sheet, and in part of marine currents bearing icebergs during a submergence of 

 some 450 feet. The supposed glacial drift about Birmingham and the concen- 

 tration of boulders at Wolverhampton were regarded as due to the former agent, 

 while the deposits at Cromer and the distribution of Lincolnshire chalk across 

 southern England was due to the latter. The supposed esker at Hunstanton was 

 held to be simply a sea-beach, and the London drift deposits to be of aqueous 

 origin. Thus the rival theories of floating icebergs and of land glaciers were both 

 true, the former for middle and southern England, the latter for Scotland, Wales, 

 and the north of England ; and the line of demarcation was fixed by great 

 terminal moraines. The paper closed with an acknowledgment of indebtedness to 

 the many geologists of England and Ireland who had uniformly rendered most 

 generous assistance to the author during his investigations. 



