W. A. E. Ussher — Post- Tertiary Geology of Cornwall. 109 



Mr. Spence Bate (Trans. Dev. Assoc, for 1866) alludes to the 

 occurrence of flints in moorland around Dosniare Pool, Curza 

 (? Crousa) Down, on the top of Maen rock, at Constantine, and on 

 Trevose Head. 



The flints occurring in the Eaised Beaches will be noticed in the 

 section devoted to the latter further on. 



As the present drift of shingle from W. to E. is the reverse of 

 that which the presence of chalk flints in the recent beaches would 

 lead us to expect, we may conclude that they were obtained by the 

 destruction of the raised beaches, and explain their occurrence in the 

 latter by either of the following hypotheses : first, that the set of 

 the wind-waves during the formation of the Baised Beaches was the 

 reverse of the present, as Mr. Godwin-Austen suggests (Q.J.G.S. 

 vol. vi. p. 87) ; or, secondly, that during the Pliocene or part of 

 the Pleistocene Period, prior to the formation of the raised beaches, 

 the land stood at a much greater elevation, and the English Channel 

 valley as dry land " served to connect the British Islands with 

 France, etc." (Godwin-Austen, op. cit.) ; that a large part of its area 

 was drained by rivers and streams flowing westward, and carrying 

 Cretaceous and other easterly derived detritus in that direction, 

 which detritus, on the submergence of the valley, was incorporated 

 by the Pleistocene sea in the beaches then successively marking its 

 advance, till the culmination of the subsidence at levels marked by 

 the Eaised Beaches. 



Notes on Glacial Hypotheses. 



Although the Glacial epoch has left no direct evidences of its 

 changes in Devon and Cornwall, it is scarcely possible that either 

 county remained uninfluenced by them. The very fragmentary 

 relics of deposits formed during the existence of a previous and very 

 different configuration seems to call for some such powerful denuding 

 agencies as torrential surface waters, consequent on the termination 

 of rigorous conditions of climate. 



The Bev. 0. Fisher (Geol. Mag. 1873, Yol. X. p. 163) ascribes the 

 reversal of lamina? in schorlaceous granite, in Carclaze Mine, to the 

 passage of ice over them. But such phenomena, as I have elsewhere 

 (Q J.G.S. 1878, vol. xxxiv. p. 49) endeavoured to show, furnish no 

 proofs of ice-action in the South-west of England. Stria? or 

 moutonneed surfaces have not been detected in Devon or Cornwall. 

 The grooved face of rock near Barlynen Abbey, North Devon, 

 ascribed by Prof. Jukes to ice-action (Geol. Mag. Vol. IV. p. 41 ; 

 vide Whitley, 32nd Ann. Bep. B. Inst. Corn.), is merely a voluted 

 bedding plane, a structure not unfrequently met with in Devonian 

 and Culm-measure rocks, and exhibited by some beds in an adjacent 

 quarry. 



If Cornwall was at any time subject to extreme glacial conditions, 

 its highlands were not submerged during the Glacial epoch, nor 

 were its borders invaded by a foreign ice-sheet ; for traces of 

 submergence would be found in the one case, and foreign ice-borne 

 materials in the other. Positive evidences of local glaciation are 



