472 MR. R. M. DEELET ON THE PLEISTOCENE 



Though I have named it the Later Pennine Boulder- clay stage, it 

 must not be supposed that Pennine rocks always form a large per- 

 centage of the deposit ; indeed it is frequently almost wholly formed 

 from the subjacent rocks, with the addition of a few Pennine, Cam- 

 brian, or even Cumbrian erratic boulders. My reason for calling it 

 Later Pennine is more to mark the return of local ice- action, inter- 

 rupted during the Middle Pleistocene epoch by the formation of the 

 Great Chalky Boulder-clay, than to indicate its lithological charac- 

 teristics. 



The deposits formed during the Later Pennine Boulder-clay stage 

 resemble those of Older and Middle Pleistocene times in having been 

 formed by ice which came from the same quarter, but they differ 

 from them in many other most important respects. The Older 

 Pleistocene Boulder-clays are partly sedimentary, while these later 

 deposits are almost entirely unstratified, and when pebbles or boulders 

 occur, a fair percentage of them are of flint. During the Middle 

 Pleistocene epoch Cretaceous rocks were not carried many miles up 

 the northerly tributaries of the Trent, so that in these valleys this 

 test for age is not always available. 



Whenever the rocks upon which the Boulder-clay rests are exposed 

 they are seen to be more or less contorted. Sometimes this crushing 

 has not been sufficient to entirely obliterate their stratification and 

 convert the rock into a morainic Boulder-clay. These signs of 

 disturbance in many cases become so great as they are traced 

 horizontally, that the rock passes into true moraine ; and when this 

 is so, the Boulder-clay passes into contortions both horizontally and 

 vertically. It is therefore evident that the contortions seen in 

 the surface-portions of so many sections are of the same age as the 

 Later Pennine Boulder-clay, and were formed by the same ice-sheet. 



Unlike the earlier deposits, these subglacial moraines are strictly 

 conformable to the major features produced by the previous inter- 

 glacial erosion, and in this respect offer a marked contrast to the 

 preceding formations, which may be described as generally conform- 

 able to the preglacial land-surface, and to have had the more modern 

 valleys, in which the Later Pennine Boulder-clay occurs, excavated 

 through them. 



In many cases it is scarcely correct to call this moraine a 

 Boulder-clay; for it is occasionally quite free from clay, consisting 

 of gravel and sand so disturbed that all traces of original stratifica- 

 tion, if they ever existed, have been destroyed. 



All the Boulder-clays and gravels from the Early Pennine down 

 to the Interglacial River-gravel have been crushed at the surface or 

 even partially converted into newer Boulder-clay. Flints have by 

 this means been introduced to considerable depths into the surface- 

 portions of non-flinty deposits. It is therefore never safe to say 

 that that rock is present in a Boulder-clay when found near the 

 surface, until it has been positively ascertained that the section 

 shows 'no traces of disturbance by Middle or Newer Pleistocene ice. 



In addition to the evidence furnished by the presence of erratics, 

 the direction in which the ice -sheet moved is indicated by the trend 



