Geological Society. 373 



containing "Observations on a Species of Tremolite found 

 in Coinwall," was read. 



This mineral occurs in a dark sreen serpentine rock, 

 forming the ridge called Clicker tor, in the neighbourhood 

 (if Li<keard. It is accompanied by asbesl. On analysis it 

 appears to be composed of 

 6-2-2 sdica. 

 14'1 lime. 

 12*9 magnesia. 

 5' 9 oxide of iron. 

 10 water. 



a trace of oxide of manganese and of soda. 



&6-1 

 3'9 loss. 



100-0 



The continuation of Dr. MacCulloch's paper on the 

 Geology of different parts of Scotland was read, and thaijks 

 were voted for the same. 



The granular quartz of Isla appears to be precisely the 

 same rock as the sandstone of Jura already described. 

 From the observations of Prof. Jameson, coinciding with 

 those of Dr. MacCulloch, it appears to alternate with 

 mica slate and clay slate, and with a very important forma- 

 tion of limestone. This limestone is more or less granular, 

 and contains no organic remains, nor any beds of fetid 

 limestone : when inclosed between beds of clay slate, it is 

 of a dark blue colour ; when in contact with mica slate, it 

 is gray or white: both varieties pass insensibly into the 

 slate within which thev are inclosed ; and the limestone, 

 the schistus, and the sandstone, are evidently members of 

 one formal ion. 



The siructurc of Schehallien is the subject of the next ar- 

 ticle. This mountain consists of a central ridge in vertical 

 strata, flanked on every side by beds of mica slaie near|y ver- 

 tical, and containing subordinate beds of limestone. The 

 rock composing this central ridge, though it has been de- 

 nominated granite by some mineralogists of no mean name, 

 is in fact the same as the granular quartz of Jura, being 

 composed of highly compacted grains of quartz, with inter- 

 spersed grains of earthy felspar. The same quartz rock 

 appears in the valley of the Lyon, to the south of Schehal- 

 lien, and it seems that the mica slate alternates with beds of 

 quartz rock, and is iherefcre of the same ocra as this latter. 



The vicinity of Crenian, wliicb is the subject of the next 



article, is remarkable for presenting nearly vertical beds of 



A a 3 vvell 



