W. A. E. Ussher — Post-Tertiary Geology of Cornwall. 209 



says, " A time when the degradation of the surface proceeded much 

 more rapidly, and when fragments of rock far exceeding the motive 

 power of any rainfall were conveyed down slopes along which only 

 the minutest particles of matter are now carried" (vide 9 c). Such 

 conditions of long-continued subaerial waste are likely to have 

 prevailed, as Mr. Godwin-Austen suggests (Q.J.G.S. vol. vi. p. 93, 

 etc.), during a greater elevation of the (South) West of England. 



The rough appearance of stratification sometimes noticeable in the 

 Head [(1) through the horizontal lie and apparent regard to gravity 

 in distribution of its contained fragments, vide 3b; 5 b; 13 a; 20 d ; 

 (2) through strips of loam or clay without stones, as in the higher 

 cliffs bordering Pra Sands, and 15 b ; (3) through percolation of 

 water carrying down overlying substances to a certain horizon, as 

 17 e ; (4) through distribution of colouring matter, as 5 b, 13 a] may 

 in many cases be due to fluviatile deposition, to which Mr. Godwin- 

 Austen referred the Head at Swanpool (5 d) and other places. 



We cannot suppose that no fluviatile deposits were formed during 

 this period of subaerial waste ; judging from the pell-mell distribu- 

 tion of angular fragments in the torrential gravels of the present 

 streams, in their higher reaches, it is only reasonable to expect that 

 similar deposition would then have taken place on a much larger 

 scale, and that its traces would be found in the present area of the 

 county which would only represent the highlands of its former 

 extension. 



Raised Beaches. — The general consolidation of the old beach mate- 

 rials, occasionally into a very hard rock (vide 6 c; 16g,h; 18), renders 

 their detection, even as fragments on a level with the surface of the 

 present beach, comparatively easy ; where, however, the process of 

 consolidation was interfered with by the accumulation of the Head, 

 the beach material seems to have been swept away, and in some 

 cases to have left traces in occasional pebbles at or near the base of 

 the Head (vide 5 a; Qa; 16 a ; and perhaps 19 g). Even where the 

 raised beach is well developed, the upper part has been sometimes 

 mingled with the base of the overlying talus (13 b). Angular frag- 

 ments are occasionally found in the raised beaches (16/). The 

 above observations serve to explain the appearance of beach material 

 on Head, S. of Perranuthno (9 g), as, in an adjacent section (9/), 

 the Head is represented by pebbles and subangular fragments. On 

 Bray Hill (20 b), 6 inches of consolidated sand rests on 2 to 3 feet of 

 Head ; but the latter is represented in an adjacent spot by con- 

 solidated sand with angular fragments of slate, and land shells (20 c) ; 

 so that the old sand drift may have taken place on the beach plat- 

 form after a little talus had been shed upon it during the earliest 

 symptoms of elevation. 



It is often difficult, where old consolidated blown sands occur, to 

 distinguish their junction with underlying raised beaches, as pebbles 

 and fragments of Mytili, Patellce, etc. (16 i; 11 f, g ; 18) may 

 have been cast upon the dunes by storm waves ; for their presence 

 and linear arrangement in recent blown sand (19 e) would seem to 

 be due to protracted gales from the same quarter. 



DECADE II. — VuL. VI. — NO. V. 14 



