68 Geological Society : — 



of thin seams of pipe-clay is rejected as a test of horizons, as 

 affording only ambiguous evidence. 



2. A similar succession is shown in a section drawn from Wel- 

 lington College Well through the sand-pit at the brick-yards by 

 Ninemile Ride (base of the Middle Clays exposed), Easthampstead 

 Church Hill (with more recent data), and Bill Hill (Easthampstead), 

 to the S.W. Railway at Bracknell, bringing the higher beds of those 

 two hills into the horizon of the Upper Sands. Further notes are 

 also added to those of the author's 1888 paper (Q. J. G. S. vol. xliv.) 

 on the Ascot Hills, Englefield Green, and Windsor Park, where the 

 transgressive relation of the Bagshot Beds to the London Clay is 

 maintained. 



3. In conclusion, the author points out that the new well-sections 

 confirm the trustworthiness of that at Wellington College as a vertical 

 datum-line ; he criticizes the views of previous writers and maintains 

 that, with the aid of Lieut. Lyons' recently published contour-map, 

 we can now discriminate between the effects of contemporaneous 

 and post-Eocene earth-movements in the area ; and that the physical 

 history of the Bagshot Beds, which he has himself propounded, is 

 substantiated by the stratigraphical evidence. 



November 26. — Dr. A. Geikie, F.R.S., President, in the Chair. 



The following communications were read : — 



1. " Account of an Experimental Investigation of the Law that 

 Limits the Action of Plowing Streams." By R. D. Oldham, Esq., 

 A.R.S M., P.G.S., Deputy Superintendent of the Geological Survey 

 of India. 



The author brings forward evidence derived from experiments in 

 support of the views expressed in a paper submitted to the Society 

 in 1888. His apparatus consisted of a sloping trough, through 

 which various amounts of water containing definite percentages of 

 sand could be sent. The lower end of the trough issued on to a 

 semicircular platform. 



In three experiments with the trough at a slope of 1 in 20, and 

 with the same work to be done in each case, the resulting slopes 

 after sand had accumulated in the trough were as follows: — With 

 one part of sand to 42 of water, a slope of 1 in 40 ; with 1 of sand 

 to 28 of water, 1 in 20 ; and with 1 of sand to 14 of water, 1 in 

 13-3. These slopes were obtained when a condition of equilibrium 

 had been maintained so that the water was just able to transport 

 its burden. By increasing the supply of water from 14 : 1 to 42 : 1, 

 the original slope was eventually obtained. 



On the fan formed on the horizontal platform variations in the 

 water-supply did not produce nearly so marked an effect as in the 

 confined channel, and the slope varied considerably in different 

 directions. 



After a time a channel was cut back into the fan, and its sand 

 swept forward and deposited as a secondary fan in front of the first ; 



