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EEV. A. IKYING ON THE PHYSICAL HISTOKY OF 



Discussion. 



The President observed that of the many interesting matters 

 discussed the most striking was the discovery of freshwater Diatoms. 

 He uttered a caution, however, as to the possibility of their not 

 being of the age of the beds in which they were found. 



Mr. Monckton allowed that the paper contained many new facts. 

 His own hypothesis certainly differed from that of the Author, who 

 had a better working-case than on a previous occasion. Indeed he 

 might not be far from beiug correct, though there were still reasons 

 for doubting this. As regards St. Anne's Hill, he admitted that 

 possibly there might be no pebbles in situ in the Lower Bagshots, 

 but he thought that appearances which mislead here might do so 

 at other points. In the Middle Bagshots there are undoubtedly 

 marine shells to deal with, the bivalves usually having both valves 

 united. He admitted the occurrence of pebbles in the Upper Bag- 

 shots on Pirbright Common, having there found pebbles with fossils 

 attached to them. 



Referring to the Wellington-College section he criticized the lines 

 as there shown, remarking that in point of fact the lines of the 

 London Clay and the Bagshots coincide in their rise and fall. The 

 London Clay thickens steadily eastwards — at Wokingham under 

 300 feet thick, at Chertsey nearly 400 feet, at Claremont 450 feet. 

 He doubted the views of the Author as to there being unconformity 

 at one place, e. g. Wokingham, and passage-beds at another, e. g. the 

 Brookwood well-section. Clays occur at the base of the Lower 

 Bagshot, both where unconformity is alleged and where a passage- 

 bed is said to exist. He suspected that in well-sections the Author 

 recognized a passage-bed, and on the surface an unconformity. 



Mr. Heeries claimed certain beds referred by the Author in his 

 Wellington-College section to the Middle Bagshots as really belong- 

 ing to the Lower Bagshots, in which case the surfaces of the London 

 Clay and Lower Bagshots would conform. He criticized the Ascot 

 section, especially the alleged valley of erosion ; he regarded the 

 depression in the London-Clay surface there shown as in reality due 

 to dip, since the Chalk is actually 67 feet more below O. D. here 

 than at Wokingham. Referring to the discovery of Diatoms, he 

 saw no reason why there might not be intercalations of fresh- 

 water beds in the marine Middle Bagshots. He still maintained 

 that the clays in the California brickfield belong to the Lower Bag- 

 shots, which usually contain a clay-bed. 



Mr. Hudleston complimented the Author on his perseverance in 

 again ventilating this subject. We might agree to the general pro- 

 position, but not to the reasons brought forward in support of it. 

 Mr. Irving was determined to establish an overlap on the flanks of 

 the basin ; a year and a half ago this was to have been effected by 

 means of certain anticlinals. The anticlinal in the Wellington-College 

 section was now given up, and he was sure that the anticlinal at 

 Aldershot would have to share the same fate. This would be shown 

 in detail to the Society by Lieut. Lyons, R.E., now unfortunately 



