GEOLOGY 



these terraces in their present position has often materially changed the 

 geographical features ; for instance, the present peninsula of St. Anthony 

 in Roseland, above two miles in length, was before the uprise an island 

 as is demonstrated by the deposits of sand charged with marine shells on 

 the neck of the peninsula ; while the peninsula of Pendennis, forming 

 the opposite front of the entrance to the Falmouth estuary, has similarly 

 emerged from the sea which completely encircled it. 



The antiquity of these old beaches is still further borne out by their 

 frequently being overlain by the material which has long been known 

 m Cornwall, and to geologists generally, as head.' It is sometimes 

 stratified, and may contain beds of sand and fairly rounded gravel ; 

 more often however the tendency to stratification is but slight, and it 

 presents an irregular accumulation of stones, mostly angular, occasion- 

 ally subangular. Such an accumulation is made up of material similar 

 to the subsoil of the district. If this subsoil were transported from 

 higher to lower levels it would probably form a deposit similar to the 

 so-called head,' which often merges so gradually into the subsoil as 

 not to be separable from it. That the surface burden which forms the 

 subsoil is ever creeping to lower levels may be seen in the sections 

 afforded by the Cornish lanes, along the steeper valley slopes, where their 

 banks have been cut through soil and subsoil into the solid rock. In these 

 banks, no matter in what direction the lower strata are dipping, the upper 

 surface invariably bends down the hill, the downward drag of the superficial 

 accumulations involving the solid rock in its creep. The action of rain- 

 wash in the passage of debris to lower levels has already been alluded to 

 but it is evident that modern processes are not evolving the tumultuous 

 and stratified accumulations of 'head' such as are common features along 

 the sea front, and have acted as a protective covering to the raised 

 beaches. An explanation must be sought elsewhere. 



In Pleistocene times the whole of Britain, except its highest 

 peaks, as far south as the Bristol Channel, was probably buried beneath 

 a mantle of ice, and during these arctic conditions the face of the 

 country was profoundly modified by the grinding effects of the glaciers 

 which over-rode it. While nowhere in Cornwall is there evidence 

 of the county having been invaded by that ice cap, its proximity to 

 the edge of the ice field must necessarily have entailed the rigours of an 

 arctic climate, under which the land was incapable of supporting any but 

 the sparsest vegetation. In winter, not only would the higher ground be 

 swathed beneath a covering of snow, but the crumbling debris which so 

 deeply covers our slopes would be frozen for many feet below the surface. 

 The melting of the winter snows and the ice which bound the frozen 

 soil, acting on a surface unchecked by vegetation, would involve a 

 sweeping of material down the slopes that would amply account for the 

 abnormal character of that deposit. In its downward course it has filled 

 the hollows on the coast line and covered the shelf of the ancient beach 

 ) which it has afforded a protection, so that the thickest deposits of 



