PITCHSTONE. 525 



extensive family; although it presents, at the 

 same time, some very remarkable differences. 

 It is also important to remark, that it is only 

 found in those districts where the rocks of that 

 family occur. 



It has been said to exist in the form of strata, 

 in foreign countries ; but no example of that dis- 

 position is found in Britain. It will be more 

 fully shown under the head of jasper, that cer- 

 tain varieties of that rock, which are disposed in 

 a stratified form, have been mistaken for pitch- 

 stone ; and it is more than probable, that all the 

 other instances of a supposed stratification, are 

 examples of veins, like many of those of the 

 trap family, holding a course parallel to the in- 

 cluding strata. 



In this country, it occurs invariably in the 

 form of veins, traversing all the rocks among 

 which it is found, and, where it is in company 

 with stratified substances, crossing them in an- 

 gular directions, or insinuating itself in a parallel 

 manner between the strata. The instance of the 

 Scuir of Egg, is an apparent, rather than a real, 

 exception, to this rule ; as there is no reason to 



