Reports and Proceedings — Geological Society of London. 87 



Geological Societt of London. 



L— Dec. 23, 1891.— W. H. Hudleston, Esq., M.A., F.R.S., Vice- 

 President, in the Chair. — The following communications were read : 



1. "On Part of the Pelvis of Polacanthus." By E. Lydekker, 

 Esq., B.A., F.G.S. 



The specimen desci-ibed in this paper was acquired by the British 

 Museum from the collection of the late Mr. Beckles, and is from the 

 Wealden, probably of the Isle of Wight. It is the central part of 

 a Dinosaurian ilium, with portions of sacral ribs attached. 



The point of special interest is a flat plate of bone, evidently a 

 portion of dermal armour, resting on the upper border of the ilium ; 

 and this suggests comparison of the specimen with the dorsal shield 

 of Polacanthus Foxii. Such a comparison shows that the present 

 specimen belonged to a Dinosaur closely allied to, if not identical 

 with, P. Foxii. 



2. " On the Gravels on the South of the Thames from Guildford 

 to Newbury." By Horace W. Monckton, Esq., F.G.S. 



The author stated that the greater part of the hill-gravel in the 

 district referred to belonged to the Southern Drift of Prof. Prestwich, 

 and that the valley-gravels for the most part consisted of material 

 derived from the Southern Drift. Small patches of Westleton Shingle 

 and Glacial Gravel occurred near Reading and Twyford. 



He divided the Southern Drift into three classes : — 



1. Upper Hale type, characterized by the abundance of small 

 quartz pebbles and the scarcity of chert. 



2. Chobham Ridges type, with abundance both of small quartz 

 pebbles and chert. 



3. Silchester type ; quartz scarce, and chert very rare or altogether 

 absent. 



He described the localities at which these types occurred and their 

 limits of distribution, and then referred to the Glacial Gravels of the 

 Tilehurst plateau, which he believed to have been deposited before 

 the excavation of the valley of the Thames between Reading and 

 Goring. 



The author then dealt with the valley-gravels, which he believed 

 to be mainly derived from the hill-gravels of the immediate neigh- 

 bourhood, and showed how the various types of hill-gravel had 

 contributed materials for the valley-gravels. He explained that, 

 with the possible exception of the Westleton Shingle, he entirely 

 rejected the theory of marine action in connexion with the formation 

 of these gravels, and thought that the Glacial Gravels were probably 

 for the most part due to floods during melting of large quantities of 

 ice. The remaining gravels, he believed, had been spread out by 

 water in valleys ; as denudation proceeded, the gravel, by protecting 

 the ground upon which it lay, cam,e to stand out as the capping 

 of the plateaux and hills ; as the gravel itself was denuded, the 

 materials were carried to lower levels, forming new gravels ; and 



