174 Dr. Berger on the physical Structure 



It will have been remarked, that calamine or carbonate of zuic, 

 so common in stratified limestone, is found in no part of Cornwall 

 that I am aware of, although blende, or sulphuret of zinc, occurs 

 pretty abundantly in the veins. 



Those who know the geological situations of coal will not expect 

 to find it in Cornwall. There is at Bovey in the eastern part of 

 Devonshire, a kind of brown coal or bituminized wood (hrann- 

 kohle) which contains some very remarkable substances. I refer 

 however for a full account of this substance to the interesting memoir 

 of Mr. Hatchett.* 



According to Klaproth, asphaltum or indurated bitumen has been 

 found somewhere in Cornwall in granite, at the depth of ninety 

 yards, f I am not acquainted with the locality, but I should suppose 

 that the presence of this inflammable principle in that situation must 

 be owing to some local and accidental cause. 



Among the substances that are combined w^ith the dllFerent 

 metals of which the mineral deposits of Cornwall are composed, 

 there are two which merit particular notice, both on account of their 

 very general occurrence, and also because they appear in cer- 

 tain circumstances to act considerably up^on the rocks with which 

 they are in contact, altering their texture, and distintegrating them, 

 as if they had been exposed to acid vapours. These two substances 

 are sulphur and arsenic. 



This change of appearance in the rock in contact vv^ith the veina, 

 and which sometimes extends pretty far, takes place principally 

 where the ore is strongly combined with sulphur. It is found to 

 continue for some distance yrom the actual contact of the orCy so much 

 so, that in following a barren vein, if we come to a place where the 



* Philosophical Tiansactions, 1304, part 2. f Miner. Obser, p. 32. 



