Geological Sociefy. 71 



Mauritius, ami is 150 miles in circumference, appears to 

 be chiefly of volcanic composition. An -active volcano still 

 exists. Although beneath the tropics, perpetual snow and ice 

 cover the summits of some of the mountauis, which rise to an 

 elevation of 10,000 feet. Lieut. Short observed basaltic co- 

 lumns of great height exposed in some parts of the island, and 

 found olivine, lava, zeolite and puzzolana abounding through- 

 out the rocks. 



A Notice was read respecting the Pebbles in the Bed of 

 Clay which covers the new red Sandstone in the South-west 

 of Lancashire, by John Bostock, M.D. V.P.G.S. 



A Pa})er was read containing a Description of a Section of 

 the Crag Strata at Bramerton, near Norwich, by Richard Tay- 

 lor, Esq. Communicated by John Taylor, Escj., Treas. G.S. 

 — This Paper was accompanied by a Sketch of the Crag Beds 

 at Bramerton, resting upon the upper Chalk, and a Table was 

 subjoined containing the respective thicknesses of the series of 

 Beds, with a List of such organic Substances as belong to each. 



A Paper was read On the Geology of Rio de Janeiro, by 

 Alexander Caldcleugh, Esq. M.G.S. — The mountains in the 

 neighbourhood of Rio de Janeiro are for the most part com- 

 posed of gneiss, intersected b}' granite veins. A siliceous sta- 

 lactite 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, v/hich in Brazil constantly trickles 

 down the bare sides of the hills, often reaches a temjierature 

 as high as 14-0^ or 150° of Fahr. : this warm water descending 

 on decom})osing sti'ata of gneiss, such as is the case with that 

 from which these speciniens are taken, seizes the potash of the 

 felspar, and then acts upon the quartz, and forms a siliceous 

 stiilactite. 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 shov/n to be the case with car- 

 bonate of lime, may in a great mca^3ure depend on the tem- 

 perature of the alkaline solvent. 



June 27. — A Paper was read, entitled "■ Observations on 

 the Quartz Rock Mountains of the West of Scotland and 

 North of Ireland, more particularly those of Jura, with an Ac- 

 count of the ancient Beaches and Tra}) Dikes of that Island, 

 accompanied by a Plan and Sections." — 'Yhc 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 10,2G0 feet. The similarity and 



singularity 



