74 



itself consists of slate. The pieces of flint that I show, some of 

 which are worked, and that I found on lower levels, undoubtedly 

 came from Ireland, and were brought to Wales by glaciers, 

 which necessarily spread over Gower. 



The deposits associated with the raised beach in Gower are : — 

 (i) beach shingle, with shells of recent species, cemented into a firm 

 mass ; (2) on this, a reddish sand, probably blown sand ; (3) a 

 rubble of strictly local rock fragments — upon this series rest glacial 

 deposits. In South Pembrokeshire the same order of supposition 

 is found, and probably on Caldey Island, near Tenby. On the 

 shore of this island are large erratics of igneous origin. — 15. 



In 1890 I asked, "Must we not believe that this ice-sheet 

 [described by Prof. Hicks as at least 1,000 feet thick on St. David's 

 Head, and thick enough to have crossed Preselly mountain, 1,760 

 feet high], advanced into the Bristol Channel, blocking its waters 

 and covering parts of Somerset with secondary and sedentary ice, 

 and causing subsequent lakes and morasses ? " 



In 1907, I heard from Mr. F. W. Harmer, F.G.S., that he had 

 received from Mr. Horace Woodward a copy of my paper, and that 

 " he finds the existence of ice blocking the Bristol Channel, and 

 covering the S.W. of England, necessary to explain some of the 

 phenomena of that region." 



As regards the subject under consideration, few things are more 

 important than a knowledge of the origin and distribution of gravels. 



The great expanses of river-gravel in England are generally 

 found in districts where there is much old marine or glacial gravel 

 from which it has been largely derived A large portion of the 

 Thames valley gravel is only derived from pre-existing glacial gravels 

 which are themselves made up in great part of old shingles 

 belonging to the tertiary and triassic periods. — 16. 



The great bulk of the silicious sand on the floor of the Irish 

 Sea is to be derived from the vast deposit of drift formed during the 

 glacial period. — 17. 



Samples of the sand have been examined by Mr. Clement Reid 

 who says there is little doubt that the bulk of the material has come 

 from the breaking up of pre-existing glacial deposits. — 18. 



At one time Mr. Monckton was of the opinion that glacial 

 gravels probably never extended more than a mile or two south of 

 Reading, and that since their deposition that valley has been 

 excavated to a depth of 160 feet. — 19. 



He has since observed that in the plateau-gravels of several 

 localities south of the Thames erratics of the glacial drift occur, 

 quartzites and sand-stones, black chert pebbles, white quartz and 

 occasional boulders of igneous rock. Such localities are Tilehurst, 

 Reading, Cookham, Wimbledon, etc. — 20. 



15 — 1909. A. L. Leach. P.G. A,, xxi., 188. Mem. Geol. Survey, 

 " The Country around Swansea." 

 16— Horace Woodward. Geol. of E. & W., 1st ed., p. 328. 

 17 — Hardman. Glac. Mag., ii., 75. 

 18— Ibid. 



19 — Glac. Mag., i., 53. 



20 — Glac. Mag., ii., 20. 



