Rcv. T. G. Bonney — Pitchstones and Felsites of Arran. 507 
the sea shows (I.) the laminated base of tbe felstone : (II.) the sarae 
of a vitrified aspect, and streaky, rather spkerulitic structure ; (III.) 
pitcbstone; (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 wkether this particular piece of pitch- 
S. N. 
Fig. 4. — Section showing 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, 
tliough 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 rocks ; undoubted ordinary 
felsite (though indurated and altered) being within an inch of fairly 
characteristic spherulitic felsite: but careful 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 irregulär intrusive-looking masses of rock, which, on 
olose 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 otlier 
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, 
1 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 
