Mr. Aikin on Withcritc found in Shropshire. 439 



south as the parallel of Bishopscastle. The general elevation of this 

 tract above the Severn varies from 800 to above 1500 feet. It is 

 completely intersected by two strait and simple vallies, the direction 

 of which is about north-east and south-west, and several smaller 

 ones parallel to the larger descend from the interior towards the 

 north and south. The principal rock which presents itself is grey- 

 wakke-slate, in beds which run north by east and south by west, 

 rising at an angle of about 50° east by south. The colour of the 

 rock where it has not undergone decomposition, is bluish or greyish 

 black, probably from a mixture of carbon, for by exposure to the 

 air it passes to a pale yellowish-grey, with a few spots of oxide of 

 iron. Its cross fracture is dull, but its longitudinal fracture presents 

 numerous small spangles of mica. The upper beds, or rather the 

 superficial parts of many of the beds, are in the state of shale, that 

 is, they are shattery, soft, and more or less decomposed. No true 

 veins ever occur in this shale, and even veins of considerable size 

 and regularity in the compact part of the rock, terminate almost 

 immediately on coming in contact with the looser part. 



It is in this compact greywakke-slate, and chiefly on the western 

 side of one of the highest hills called the Stiperstones, that the 

 principal lead mines of the county occur. Of these, that which is 

 called the Snailbach mine, is the most important for its metallic 

 produce, and is the only one in which witherite has hitherto been 

 found. 



The mine consists of one principal vein, with several strings 

 proceeding from it. Its course is nearly east and west, descending 

 at a high angle to the south : its greatest depth is about 180 yards, 

 and there are no signs of its approaching to a termination : its 

 general thickness is 10 or 12 feet, but in one particular part amounts 

 to more than 30 feet. Cavities, or locks as the miners call them, are 



3 k 2 



