StrCCESSION IN THE TEENT BASIN. 467 



distributed over the face of the countrj- indicate a period of cold 

 during which glaciers came once more from the Pennine Hills. The 

 erratic boulders of this stage distributed over the westerly portion of 

 Staffordshire show that the climate was sufficiently severe to cause 

 the combined Scotch and Cambrian glaciers to invade the westerly 

 portion of the Trent basin. I have only been able to show the 

 existence of one period of glaciation during this epoch, but there 

 might have been two or even more, separated by considerable 

 intervals of time. The impossibility of settling this point is due to 

 the lithological similarity which would exist between the several 

 deposits in spite of their different ages. 



I have not been successful in finding freshwater shells in the 

 Inter glacial Eiver-gravel ; but the evidence I shall be able to adduce 

 when that stage comes to be considered in detail, justifies me in 

 regarding them as being due to river-action. 



1. Interglacial River-gravel. 



All the deposits T have described as belonging to the two previous 

 epochs were formed during one continuous period of submergence. 

 No doubt there were considerable oscillations in the depth of this sea 

 from time to time ; but no break seems to have occurred during 

 which alluvial gravels and sands were formed until we reach the 

 present stage. 



The light thrown upon the contour of the preglacial land-surface 

 by the deposits previously described is of a very scanty nature ; 

 indeed nothing of Newer Pliocene age has yet been found. What 

 evidence there is, is furnished by the presence of Older and Middle 

 Pleistocene Boulder-clays at tolerably low levels, at some few points 

 in the vicinity of the present watercourses. 



At Sheldon Wharf (fig. 1), a few miles south of Derby, Older 

 Pleistocene Boulder-clay rests upon Keuper marl within 40 or 50 

 feet from the bottom of the modern valley of the Derwent. North 

 of Swarkestone the Chalky Clay also plunges down to a low level in 

 the valley, which is here that of the Trent. As a general rule, the 

 Boulder-clays of Older or Middle Pleistocene age will be found to 

 occupy lower and lower positions in the valleys the nearer they 

 approach the present watercourses. It would therefore seem that 

 the broader features of hill and valley were sketched out in pre- 

 glacial times, and that Newer Pleistocene erosion has, after removing 

 the greater portion of the older Boulder-clays from the low-lying 

 areas where they occurred, commenced to widen and deepen the old 

 valleys. 



Considering the great thickness of loose sand and gravel which 

 has escaped destructiop by the glaciers of the Pleistocene period, it 

 might seem strange that no trace of preglacial river-gravel is now 

 to be found, so far as I am aware, in the Trent basin. For my own 

 part, I am inclined to believe that the Newer Pleistocene erosion, the 

 traces of which are now to be considered, has been so great, and 

 has been carried on so nearly along the lines of the old valleys, 



