42 Mac Culloch on Pitchstone. 



occurring in beds under trap, have been occasionally con- 

 founded with it, as I lately remarked in a communication on 

 the subject of jasper. Under these doubts, I can only pretend 

 to give its history as far as it can be deduced from the facts 

 visible in Scotland. Hereafter, when it has been an object of 

 more accurate research, its true history will, probably, be more 

 completely elucidated. 



In its geological connexions, as well as in some of its mineral 

 characters, it approaches very nearly to many members of the 

 trap family ; although it presents, at the same time, some very 

 remarkable differences. It is also important to remark, as it 

 appears to strengthen the connexion between this rock and that 

 family, that it is found in those districts or countries where trap 

 exists. 



It has been said to occur in the form of strata in many parts 

 of the European continent ; but no example of this disposition 

 has yet been observed in Britain. Those masses which have 

 been mistaken for strata in the island of Arran, are no more 

 entitled to that name than the masses of trap which are so 

 often found similarly placed ; they are merely veins holding a 

 parallel or conformable direction to the rocks by which they 

 are included, as will be more fully pointed out immediately. 



It will also be found that the stratified pitchstones of Europe, 

 so often described, and so well known, do not appertain to this 

 species of rock, and that the whole of the observations on these 

 rocks are founded on a mineralogical error ; that they have 

 arisen from confounding the resinous looking jaspers, described 

 under that head in a preceding article, with true pitchstone. 

 These substances are, indeed, stratified ; but they differ from 

 pitchstone, not only in their several characters and chemical 

 composition, but in every essential circumstance of their geolo- 

 gical origin and position. This, at least, I may affirm of every 

 specimen of pitchstone from these strata which has hitherto fallen 

 under my inspection ; and I have little doubt that a fuller and 

 an unprejudiced re-examination of these imaginary strata, will 

 confirm these views ; by proving that they are truly jaspers, 

 and that whenever real pitchstone occurs in masses parallel to 



