Natural History. 99 



As the accumulated snow was in excess of the quantity 

 annually melted, glaciers began to descend, first of all into the 

 Irish Sea from all sides, namely, North Wales, Ireland, the 

 Clyde, and the English Lake District; and into the North and 

 Baltic Seas from the Scandinavian Mountains. Year after 

 year, the glaciers increased in magnitude, and the ice flowing 

 into the Irish Sea (which is only, comparatively speaking, very 

 shallow) coalesced, entirely excluding the water,* and finally 

 diverted the ice from the Lake District over the Upper 

 Stainmoor Pass into Teesdale, down which it flowed towards 

 the North Sea. 



In the meantime the ice from the Scandinavian Mountains, 

 advancing in a huge sheet (which would resemble the Green- 

 land Ice-cap of the present day), encroached upon the waters 

 of the North Sea,t and, after reaching our shores, the two 

 glaciers flowed down the east coast. The Norse ice brought 

 with it the boulders of rhomb-porphyry, augite-syenite, etc., 

 while the Teesdale glacier carried the boulders of Shap Granite, 

 c Brockram,' and other Lake District rocks, together with 

 boulders of carboniferous limestone from the sides of Teesdale 

 itself. It was at this stage, when the Scandinavian arrested the 

 progress of the Teesdale ice, that the bulk of the latter 

 glacier was diverted down the Vale of York and formed the 

 beautiful crescentric mounds around York, which have been so 

 lucidly described by Mr. Kendall.J These mounds are 

 terminal moraines. 



The Boulder Clays of Yorkshire and Lincolnshire, therefore, 

 not only mark the area covered by the ice, but contain boulders 

 which help to indicate the direction the ice took. 



The Norwegian ice-sheet, as might be expected, laid down 

 a moraine, and this, a line of gravel hills, extends from 

 Flamborough Head into Lincolnshire, crossing the Humber at 

 Paull. During the many oscillations of the ice front the 

 moraine was over-ridden perhaps on two or three occasions. 



* We have proof that it covered Snae Fell (2,034 feet), the highest peak in the 

 Isle of Man. Kendall, ' On the Glacial Geology of the Isle of Man.' Tn. Lioar 

 Manriinagh, 1894. 



f The bed of the North Sea, like that of the Irish Sea, is exceedingly shallow. 



I The Glaciation of Yorkshire. Proc. Torks. Geol. Soc., 1893. See also Mr. C. 

 Fox Strangways' paper in Proceedings of the same Society for 1895. 



Mr. Fox Strangways' paper (just referred to) is accompanied by an excellent 

 map showing the drift-covered area of Yorkshire, and a similar map appears with 

 Mr. A. Jukes-Browne's paper in Stuart. Journ. Geol. Soc. for May, 1885, p. 115, 

 indicating the range of the Boulder Clays in the county of Lincoln. 



