Geological Society of London. 4 3 



teraporaneons 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. 



ir._Nov. 26, 1890.— 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 Flowing Streams." By R. D. Oldham, Esq., 

 A.R.S.M., F.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, I 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 neai'ly 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 ; 

 and as this gi-ew, it cut back into the reach above, and this in turn 

 cut back towards the head of the fans, and sometimes into the 

 trough. In some cases other secondary fans were formed on the 

 margin of the main fan, but the apparatus was not large enough 

 for further formations. The general slope of the fans, both primary 

 and secondary, was -06, and that of the reach only -04, while at the 

 head of the reach, where it was cutting back into the face above, 

 there was a gradient of '08 



The general tendency of the experiments supports not only the 

 specific conclusions as to the normal form and behaviour of a river 

 which has attained a state of equilibrium, but to a greater degree 

 the fundamental assumption that a river will adapt its channel to 

 such a slope and form as will enable it to just transport a solid 

 burden cast upon it. 



2. "On the Rocks of North Devon." By Henry Hicks, M.D., 

 F.R.S., Sec.G.S. 



During a recent visit to North Devon the author obtained evidence 

 which has led him to believe that far too little importance has 

 hitherto been assigrned to the results of movements in the Earth's 



