﻿Rev. T. G. Bonneij — Pitchstones and Fekites of Arran. 507 



the sea shows (I.) tlie laminated base of the felstone ; (II.) the same 

 of a vitrified aspect, and streaky, rather spherulitic structure; (III-) 

 pitchstone; (IV.) spherulitic felsite (Fig. 4), The last has fewer 

 spherules at top and bottom. No one of these three rocks is in 

 absolute contact, each being separated by a foot or two of debris. 

 It is not quite certain either whether this particular piece of pitch- 



S. N. 



X XXX 



Fig. 4. — Section sliowing relation of Felsite and Pitchstone on Corriegills shore. 



A. Flaggy Felsite. A'. Vitrified base of Felsite. 



B. Pitchstone. C. Spherulitic Felsite. 

 D. Sandstone. X. Debris. 



stone is really in situ, as it is separated from the rest of the vein, but, 

 so far as I could make out, by clearing away the rubbish, it seemed 

 to be. In the southern bay there is only the spherulitic felsite under- 

 lying the indurated base of the felsite. The question then which first 

 suggests itself is the following, Is the spherulitic felsite a special 

 condition of the ordinary felsite or of the pitchstone, or a third and 

 distinct intrusive rock ? The evidence is as follows : A passage 

 between the pitchstone and the spherulitic felsite is nowhere seen, 

 though the former seems to have rather more spherules towards its 

 base, and the latter rather fewer spherules top and bottom ; the decom- 

 posed state of the two rocks being very similar, each forming a 

 brittle grey putty-like clay. The spherulitic felsite, however, cannot be 

 quite identical with the pitchstone, because it has a different be- 

 haviour, showing a peculiar ropy structure, like some lavas, on its 

 outer surface, and adhering to the sandstone, where it is last seen, in 

 a thin skin, with an appearance of viscid flowing, difficult to describe, 

 but very remarkable. Near here we find it apparently attached to 

 the partly vitrified base of the ordinary felsite. This at first sight 

 looked like a junction of two distinct rc^ks ; undoubted ordinary 

 felsite (though indurated and altered) being v\rithin an inch of fairly 

 characteristic spherulitic felsite: but cai'eful study of the specimen 

 and microscopic examination fail to detect a perfectly clear line of 

 demarcation. Further, on the south side of the felsite dyke, are two 

 or three small irregular intrusive-looking masses of rock, which, on 

 close examination, seems to be the spherulitic felsite in a highly de- 

 composed condition ; the matrix of part being stained a light dull 

 red ; part being quite sandy and cream-coloured, like the other 

 felsite. Still, in its mode of occurrence, it resembles the spherulitic 

 felsite on the opposite side, and the spherules in places yet remain 

 fairly distinct. 



On examining the base of the felsite in the cliff over the pitchstone, 

 I found it exhibited a vitrified appearance and banded structure, 

 with numerous not very clearly defined small spherules, and a 

 peculiar structure on the surface of the base, as if it were studded 

 with half spherules arranged in lines or sometimes agglutinated 



