74 



GEOLOGICAL NOTES— DERWENT VALLEY COUNTRY. 



that of an ice sheet which could affect such extensive 

 denudation. Its occurrence would probably be towards 

 the close of that Mesozoic period of which we have so 

 little accurate knowledge, and there seems to be no 

 •other way of accounting for the rounded character of all 

 the lower diabase-capped hills, resembling gigantic 

 roches m.outonnees. It has been established that there 

 was a further glaciation in the Western Country in Ter- 

 tiar}' or post-Tertiary times, and, assuming that similar 

 conditions prevailed on the Southern mountain ranges, 

 -one might safely conclude that the main features of this 

 •district were roughly shaped b}^ moraine-bearing gla- 

 ciers descending from the Mt. Field range, the existing 

 ■configuration of the country being due to post-glacial 

 erosion under high pluvial conditions. So far there is 

 little positive evidence in support of this theory beyond 

 the presence of a few erratics, and the steep slightly 

 terraced slopes of the Permo-Carboniferous beds where 

 they bound the valleys, a contour widely different from 

 that of rocks eroded by running water. In such a dis- 

 trict as this it is futile to expect to find the evidence of 

 polished rock surfaces, or striated pebbles and boulders, 

 for none of the rocks over v/hich the glacier would pass 

 are hard enough to offer any resistance with the sole 

 exception of the diabase, and that would be broken up 

 .-rather than smoothed. 



