^t Proceedings of Philosophical Societies* [Sept, 



Article XIV, 



Proceedings of Philosophical Societies, 



Gf:Q|.pGICAL SOCIETY. 



June 20. — A paper was read, containing a Description of a 

 Section of the (Jrag Strata at Braraerton, near Norwich. By- 

 Richard Taylor, Esq. : communicated by John Taylor, Esq. 

 Treas. GS. 



This paper was accompanied by a sketch of the crag beds at 

 Bramerton, resting upon the upper chalk, and a table was sub- 

 joined containing the respective thicknesses of the series of 

 "beds, with a list of such organic substances as belong to each. 



A paper was also read, on the Geology of Rio de Janeiro. 

 By Alexander Caldcleugh, Esq. MGS. 



The mountains in the neighbourhood of Rio de Janeiro are for 

 the most part composed of gneiss intersected by granite veins. 



A siliceous stalactite was observed by the author to form in 

 this district from the overhanging masses of gneiss, specimens 

 of which were presented to the Society. 



As the absence of hot springs makes the occurrence of these 

 stalactites of very considerable interest, Mr. Caldcleugh offers 

 the following hypothesis to explain their formation ; the water 

 which in Brazil constantly trickles down the bare sides of the 

 hills, often reaches a temperature as high as 140° or 150° of 

 Fahr. This warm water descending on decomposing strata of 

 gneiss, such as is the case with that from which these specimens 

 are taken, seizes the potash of the felspar, and then acts upon 

 the quartz, and forms a siliceous stalactite. Some of the hot 

 springs or geysers of Iceland do not reach the boiling point, and 

 perhaps the quantity of silex dissolved, the inverse of what is 

 shown to be the case with carbonate of lime, may, in a great 

 measure, depend on the temperature of the alkaline solvent. 



June 27. — A paper was read, entitled, " Observations on the 



fluartz Rock Mountains of the West of Scotland and North of 

 reland, more particularly those of Jura, with an Account of the 

 ancient Beaches and Trap Dykes of that Island, accompanied 

 by a Plan and Sections.*' 



The quartz rock is traced in a succession of districts from 

 Lerwick, in Shetland, to the county of Donegal, in Ireland ; and 

 in Jura the thickness of the mass is estimated at 10,260 feet. 

 The similarity and singularity of form assumed by quartz rock 

 mountains in districts remote from each other is deduced from 

 the peculiar construction and material of the mountain mass 

 acted upon by powerful aqueous currents. Quartz rock is of 

 great extent in the county of Donegal, where, in one instance, 



