i 7 o THE POPULAR SCIENCE MONTHLY. 



were tlie agency which scored the rocks and distributed the bowl- 

 ders over the island. In the second place, these investigations 

 have explained away, in a very complete and satisfactory manner, 

 the evidence which had been supposed to prove that there was a 

 submergence of the northern part of England and Wales during 

 an interglacial period amounting to fourteen hundred or two 

 thousand feet. 



This evidence consisted of shell-beds inclosed in true glacial 

 deposits eleven hundred feet above the sea at Macclesfield, near 

 Manchester, and fourteen hundred feet above the sea at Moel Try- 

 faen, on the northern flanks of Snowdon, in Wales. Prof. Lewis, 

 and those who have followed out the clews which he started, have 

 proved that these shell-beds were not direct deposits during a 

 submergence of the country, but rather beds washed out of true 

 glacial deposits which had been shoved along by the ice in its 

 passage over the bottom of the Irish Sea. The shells were pushed 

 up with the mud from the sea-bottom, as pebbles are known to 

 have been in so many instances. The melting of the ice fur- 

 nished the water necessary for partially working over the origi- 

 nal deposit and sorting out and stratifying the inclosed gravel 

 and shells. 



The demonstration of this theory of Prof. Lewis consists in 

 showing that the deposits of shells are limited to those portions 

 of the glaciated area which can be proved, by the transported 

 bowlders, to have been overrun by ice which passed over the 

 sea-bottom. Over this area shells are more or less mingled with 

 the till, or bowlder clay, just as pebbles are, and limited beds 

 of gravel and shells are of frequent occurrence, though the 

 shells for the most part are very much broken up. An addi- 

 tional point of evidence of great weight is found in the fact that 

 the shells are not such as would collect in the same place under 

 water. In these beds rock-haunting and mud-loving species, 

 and shallow-water and deep-water species are indiscriminately 

 mingled together. 



The course of ice movement is clearly shown on the map by 

 the lines indicated in the transportation of bowlders. Briefly 

 stated, the movements were as follows : Scandinavian ice flowed 

 westward over the shallow basin of the German Ocean until it 

 reached the coast of England from Plamborough Head to the lati- 

 tude of London. It was warded off from Scotland and the north- 

 ern coast of England by the glaciers which had preoccupied that 

 region. Scandinavian bowlders are found scattered over the east- 

 ern counties of England, and there is evidence that the ice from 

 that direction penetrated to the vicinity of London and up nearly 

 to the head- waters of the Ouse and of the South Branch of the 

 Humber. Meanwhile a glacial movement had been in progress 



