GLACIAL BEDS. 



495 



The phenomena have been described more particularly by Mr. D. Mackintosh ' 

 and Mr. W. A. E. Ussher.^ Good instances are noted at Gupworthy, near 

 Wiveliscombe, Slapton, and other places in Devon, and also south of the 

 Carclaze mine in Cornwall ; and while some appearances are due to contortions, 

 and some to the intrusion of roots of trees and the action of frosts, etc., the more 

 extensive bending-back of the slates has been attributed to land-ice or to the 

 grazing force of grounding ice-bergs. (See p. 13, and Fig. 18, p. 132.) 



Certain accumulations of angular detritus and stony loam termed " Head," seen 

 along the coasts of Cornwall and parts of Devon, are probably the equivalents of 

 Glacial deposits elsewhere.^ They are the result of great subaerial waste, and 

 suggest a more rigid climate. The Head, as pointed out by Mr. Ussher, is newer 

 than the Raised Beaches, as it frequently rests upon them. (See Figs. 85, 86.) 



Fig. 86.— The Coast towards Rosemullion Head, near Falmouth. 

 (W. A. E. Ussher.) 





Rock-platforms, and Cliffs composed of Head resting upon Raised Beach. 



In his opinion, the oldest Drifts in Cornwall are probably the quartz gravels 

 of Crousa Down, in the Lizard district. Some of the features of the country 

 have, it is thought, been produced by Glacial action.* 



Pebbles and boulders of quartz, granite, and porphyry have been found on the 

 high grounds near Poole in Dorsetshire, and also in the Isle of Wight. (See 

 Fig. 73, p. 428.) Flint-gravel occurs on Headon Hill, Brading and Bembridge 

 Downs, and in the New Forest.* 



On the south coast of England, at Brighton, and westwards, between the Chalk- 

 hills and the sea, the surface of the country is formed by a raised terrace of beds 

 locally known as the 'red gravels,' and the 'white gravels,' the former, as Mr. 

 Reid informs me, being simply due to the dissolution of Chalk fragments from the 

 latter. The gravels are, in places, overlaid by brickearth, which is somewhat variable 

 in its characters ; and they are underlaid by a marine 'Mud-deposit.' (See sequel.) 



At Selsea and Siddlesham the gravels are about 25 feet in thickness, they 

 become clayey, and contain a variety of pebbles and boulders of granite, syenite, 



1 Q. J. xxiii. 323 ; G. Mag. 187S, p. 190. 



2 Q. J. xxxiv. 52 ; see also O. Fisher, G. Mag. 1873, p. 164. 



^ Godwin- Austen, Q. J. vii. 118, xxii. i; Ussher, Post-Tertiary Geology of 

 Cornwall, 1879, pp. 10, 42 ; G. Mag. 1879, pp. 102, 109, 168, 205, 208. 



* H. C. Salmon, Q. J. xvii. 517; G. H. Kinahan, G. Mag. 1870, p. 310; 

 N. "Whitley, Glacial Action in Cornwall and Devon (Penzance), 1S81. See also 

 Dr. J. F. Berger, T. G. S. i. 99. 



* Trimmer, Q. J. x. 15; Godwin-Austen, Q. J. xi. 116; C. Evans, P. Geol, 

 Assoc, ii. 1 70; T. Codrington, Q. J. xxvi. 538. 



