266 

 CHAP. XXXIX. 



Pitchstone. 



THE printed information respecting this rock is so 

 scanty and suspicious, that I dare not borrow from it. 

 As in the case of Trap, some of the remarks on its 

 position have been warped by theoretic views ; as the 

 peculiar jaspers occurring under trap, have also been 

 occasionally confounded with it. Under these doubts, 

 I must give its history as far as it can be deduced from 

 my own observations ; hereafter, its nature may per- 

 haps be more completely elucidated ; but if I have 

 given its true history for Scotland, I must believe that 

 I have done it for the whole world. 



The first remarkable circumstance respecting Pitch- 

 stone is, its limitation to trap countries, while, even 

 in these, it is rare. In our islands, it is confined to 

 Ireland, and to Arran, Rurn, Egg, and Sky. In these 

 situations it forms veins, so decided in their characters, 

 as to permit no doubt respecting their real nature, even 

 where parallel to the including beds ; when they re- 

 semble the intruding masses of trap which occupy si- 

 milar positions. They are rarely continued for a long 

 space ; more commonly terminating abruptly among 

 the surrounding rocks ; while one instance alone of 

 ramification has occurred, in a vein in Egg, divided 

 round a mass of chert. The only mass of pitchstone 

 in Scotland, of which the true nature might be disputed, 

 is that magnificent and picturesque object, the Scuir 

 of Egg. This, however, is a substance intermediate 

 between pitchstone and basalt, and, at the same time, 

 porphyritic. Standing insulated, like a narrow irre- 

 gular wall, on the surface of a mass of trap, it does 

 not at least resemble a bed; as its mineral character, 



