ANCIENT GLACIERS IN EASTERN HEMISPHERE. 163 



carried it along. This explanation we owe to Mr. Clement 

 Keicl.* The drift-deposits of this region frequently con- 

 tain shells, but they rarely constitute what may be termed 

 a consistent fauna, usually showing such an association as 

 could only be found where some agent had been at work 

 gathering together shells of different habitats and geologi- 

 cal age. 



" Attempts have been made to correlate the deposits 

 over the whole area, but with very indifferent success. A 

 consideration of the consequences of the invasion of the 

 country by an ice-stream from the northeast will prepare 

 us for any conceivable complication of the deposits. 



" The main movement was against the drainage of the 

 country, so that the ice-front must have been frequently 

 in water. There would be aqueous deposition and ero- 

 sion ; the kneading up of morainic matter into ground- 

 moraine ; irregularities of distribution and deposition due 

 to ice floating in an extra-morainic lake ; flood-washes at 

 different points of overflow ; and other confusing causes, 

 which make it rather matter for surprise that any order 

 whatever is traceable. 



" I now turn to the valley of the Trent. We find that 

 it occupies such a position that it would be exposed, suc- 

 cessively or simultaneously, to the action of ice-streams 

 of most diverse origin. I have shown that the area to the 

 westward of Lichfield was invaded at one period by a 

 Welsh glacier, and at a subsequent one by the Irish Sea 

 Glacier, and both of these streams entered the valley of 

 the Trent or some of its affluents. From the eastward, 

 again, the great North Sea Glacier encroached in like man- 

 ner, carrying the Great Chalky Boulder-Clay even into the 

 drainage area of the westward-flowing rivers near Cov- 

 entry. 



* See Geology of the Country around Cromer, and Geology of 

 Holderness, Memoirs of Geological Survey of England and Wales. 



