1819.] Geological Society. 215 



May 21. — The Secretary gave notice that the following com- 

 munication had been received since the last meeting : " Obser- 

 vations on the geological Relations of the Environs ofTortworth, 

 Gloucestershire ; and of the Mendip Range in Somersetshire,"' 

 accompanied by a Map and Sections, by T. Weaver, Esq. 

 M.R.I.A. M.W.S. 



A paper, by the Right Hon. Lord Compton, was read, contain - 

 ing " A Description of the Rocks which occur along a Portion 

 of the South Coast of the Isle of Mull."' 



These, which are called the Carsey rocks, and consist of higli 

 precipices, which are sometimes close to the sea, and at other 

 times recede a little from it, are composed almost entirely of basaltic 

 columns. In several parts they are intersected by whin dykes, 

 of which there are three that are veiy remarkable ; they are 

 almost 120 feet in height, and varying in breadth from 04. feet 

 near the bottom to about 1 7 at the top ; they are situated near 

 together ; the first is nearly perpendicular, but the other two are 

 inclined considerably to the east. The basaltic columns which 

 compose the shore are, in some places, as much as 500 feet in 

 height. In one part, a group of these columns rises in an insu- 

 lated form out of the sea to the height of 70 feet. 



There are two very remarkable arched rocks ; one of the 

 openings is about 60 feet high, and between 50 and 60 wide ; it 

 is formed in a basaltic rock resting on green sand, and does not 

 contain any fossils ; the rock itself is from 110 to 120 feet high, 

 and there is a stratum of basaltic columns above the arch. The 

 other arch is rather higher, but considerably smaller in its other 

 dimensions. The part of the shore to which the arched rocks 

 are attached is composed of lofty basaltic columns. 



The author states that in different parts of the basalt which 

 forms the coast, he found crystallized carbonate of lime, chalce- 

 dony, quartz, different kinds of zeolite and analcime, as well as 

 a mineral which is supposed to be pitchstone. 



The reading of Mr. Taylor's paper " On the Smelting of Tin 

 Ores in Cornwall and Devonshire,"' was begun. 



June 4. — The reading of Mr. Taylor's paper " On the Smelt- 

 ing of Tin Ores in Cornwall and Devonshire," was concluded. 



The author observes that tin ore is found in two states, in 

 veins accompanied by other metals, or in detached fragments 

 dispersed through alluvial matter ; they are known by the names 

 of mine tin and stream tin respectively. Mine tin is first sub- 

 jected to the process of dressing, by which a considerable part 

 of the extraneous minerals, as well as the earthy matrix, is sepa- 

 rated. The metal produced from this kind of ore is called 

 block tin, and is less pure than that from stream tin, in conse- 

 quence of some remains of other metallic substances, of which 

 it is very difficult entirely to deprive it. Stream tin has no other 

 metallic ore mixed with it, except occasionally a little heematitic 

 iron. This furnishes the grain tin of commerce. 



