OP THE PLEISTOCENE DEPOSITS OF DEVON. 455 



character are very distinct from the present accumulation of talus, 

 and indicate changes both in climate and physical geography. 



In climate — because such a quantity of material in sites not now 

 favourable for its accumulation could scarcely be ascribed to ordi- 

 nary subaerial waste ; more marked seasons, sharper frosts, and a 

 heavier rainfall would have been more favourable to its production. 



In physical geography — because, from the position of the Head 

 on cliff-faces almost immediately backed by rocks rising in crags a 

 few yards inland from the top of the cliffs, as near Start Point, and 

 its isolation in pinnacles resting on rocky pediments separated by from 

 30 to 60 yards of beach from the present cliffs, as near Start Point 

 and on Grodrevy beach in Cornwall, a further elevation of the old 

 beach platform on which it often rests must have taken place to 

 allow of its accumulation undisturbed by storm- waves or spring- 

 tides. 



The traces of submerged-forest lands on the coasts of Cornwall 

 and Devon prove the elevation of the raised beaches to have been 

 carried to much greater heights above the sea than they are now 

 found at. The Head is more easily accounted for by the admission 

 of a colder climate, which would hardly have suited the forest-growth ; 

 so that an accompanying elevation is naturally suggested. That 

 elevation may have culminated in continental conditions ; and some 

 of the former denizens of the caves may have migrated to and fro as 

 the climate favoured them ; and Alpine Salices * may have been 

 indigenous. 



In inland districts many of the existing thick stony soils may 

 have been due to the subaerial waste of this period, and, if exposed 

 in a cliff-section, would be, in most cases, undistinguishable from the 

 coast Head. 



Torrential streams and brooks frequently exhibit trifling strips of 

 alluvia of somewhat similar character to the Head ; nor does it seem 

 improbable that the regularity and definite arrangement of the flu- 

 viatile deposits was interrupted from time to time through the fluc- 

 tuations of climate causing the prevalence of floods and hasty or 

 broadcast distribution of abraded materials, so that their relics would 

 be mistaken for soils resulting from decomposition of the subja- 

 cent rock in situ. 



The clays of Koundswell and the Head in the Bovey valley might 

 be classed in this period and regarded as roughly contemporaneous 

 with the Head ; but the Petrockstow deposit may be of much older 

 date. 



In bringing about the present state of things, a gradual subsidence, 

 accompanied by an ameliorating climate, brought the period of great 

 subaerial waste to a close, and favoured the growth of forests on the 

 old sea-bed left dry by the precedent elevation. Accordingly forests 

 flourished beyond our present coasts, and, as the amelioration pro- 

 ceeded, may have covered the interior. Little by little the blasting 

 effect of the advancing waves on the growth of timber, and the cir- 



* Pengelly, " Notes on Recent Notices of the Geology and Paleontology of 

 Devon," Trans. Dev. Assoc, for 1874. 



