ARRAN. PITCHSTONE. 413 



has been found affected by the contact of a trap vein, 

 but I know of no instance in which any similar change 

 has been remarked in granite : I need not point out 

 the very obvious conclusions that may be drawn from 

 this fact. 



Three or four of these veins are to be seen at the 

 head of Glen Catcol;* one of which is so remarkable 

 on account of its form, that I have been induced to give 

 a sketch of it.f It demonstrates the forcible separation 

 of the granite, since that rock has yielded in the direction 

 of its joints, presenting an instance very similar to one 

 already described near Coruisk in Sky. But I believe 

 geologists will now scarcely require such evidence as 

 this to prove that trap veins are posterior to the granite 

 which they traverse. I need scarcely say that veins 

 similarly situated have been called primitive greenstone; 

 and it is equally unnecessary to point out the confusion 

 produced by the use of a term so misapplied. I shall 

 therefore dismiss this subject, and proceed to consider 

 that rock for which Arran is so remarkable, being the 

 last that remains to be described, namely, pitchstone. 



THE veins of pitchstone are to be seen in different 

 parts of the island ; while detached fragments of the 

 same substance, found in many other situations, seem 

 to indicate the vicinity of others not yet discovered. The 

 most conspicuous and extensive of these yet observed, 



* The rocks at the upper part of Glen Catcol are covered with 

 the Ulva montana of Lightfoot ; a plant so little common as not to 

 be much known to botanists. Its genus may perhaps admit of a 

 question, as it presents the habits of a Tremella rather than those 

 of an Ulva. As there is no figure of it extant, I have added one 

 in Plate XXX. It is there represented in fructification, when the 

 leaf thickens and curls up ; before that period it is a thin membrane, 

 moderately undulated. 



f Plate XXVI. fig. 3. 



