Geological Society. 235 



body and the case of the instrument, through the intervention of 



the residual gas. This explanation of its action is in accordance 



with recent speculations as to the ultimate constitution of matter 



and the dvnamicaHheory of gases. 



«• 



GEOLOGICAL SOCIETY. 



[Continued from p. 156.] 

 January 24th, 1877.— Prof. P. Martin Duncan, M.B., F.K.S., 



President, in the Chair. 

 The following papers were read : — 



1. " Note on the Question of the Glacial or Volcanic Origin of 

 the Talchir Boulder-bed of India and the Karoo Boulder-bed of 

 South Africa." By H. F. Blanford, Esq., F.G.S. 



The author, referring to a doubt expressed by the President in a 

 paper on Australian Tertiary Corals as to the glacial origin of the 

 Talchir Boulder-bed, indicated that the hypothesis of its formation 

 by the action of local glaciers under present climatal conditions 

 would require the elevation of the whole region to the extent of 

 14,000 or 15,000 feet, and the assumption that the denudation of 

 this great mountain mass was so moderate that large tracts of the 

 ancient surface are still preserved at levels now only a few hun- 

 dred feet above the sea. This the author regarded as very im- 

 probable. He assumed that the President, rejecting the evidence 

 adduced by various writers in favour of the glacial origin of the 

 Talchir and Karoo Boulder-beds, was inclined to fall back upon the 

 notion of their being of volcanic origin, and quoted a letter from 

 Mr. King, who had described the Talchir rocks of Kamaram as trap- 

 pean, in which that gentleman stated that the rocks so interpreted 

 by him prove to be dark green and brownish mudstone. He cited 

 further evidence of like nature, and concluded that the ascription of 

 a volcanic origin to these boulder-beds was probably in all cases 

 due to similar misinterpretations. 



2. " On British Cretaceous Patelloid Gasteropoda." By John 

 Starkie Gardner, Esq., E.Gr.S. 



3. " Observations on remains of the Mammoth and other Mammals 

 from Northern Spain." ByA.LeithAdams,Esq.,M.B.,F.B.S.,F.G.S. 



February 7th, 1877.— Prof. P. Martin Duncan, M.B., F.E.S., 

 President, in the Chair. 



The following paper was read : — 



1. " On the Chemical and Mineralogical Changes which have 

 taken place in certain Eruptive Bocks of North Wales." By John 

 Arthur Phillips, Esq., F.G.S. 



In this paper the author described the felspathic rock of Pen- 

 maenmawr, which has been erupted through Silurian strata, and 

 rises to a height of 1553 feet above the level of the sea. The rock, 

 which is composed of crystalline felspar with minute crystals of 

 some hornblendic mineral, is fine-grained and greenish grey, divided 

 into beds by joints dipping north at an angle of about 45°, and 

 again divided by double jointings, sometimes so developed as to 



