328 Dr Boud’^ Comparison of the Volcanic RocJcs of France 
semblance is not so great as in the rock of Lamlashc The 
porphyries of the Giiieton Hills, near Haddington, bear only a 
slight resemblance to those of the Mont d’Or, while the va- 
rieties found in the Pentland range, are of a different nature, 
4. The greater part of the rocks of Arthur Seat have the same 
arrangement, and are of the same species as those in the volcanic 
districts of Auvergne and the Vivarais. The form of the hill, its 
rising suddenly in the midst of a comparatively flat country, 
its terraced aspect, its various lava-like rocks, and other circum- 
stances, would seem to shew that it has been a submarine vol- 
cano. But the rocks of Salisbur}^ Craig are of a different na- 
ture. I did not meet with any greenstone rock like that of the 
Craig, in the volcanic country of France, nor any lava, which 
contained such quartz-crystals, and iron-stone veins, as occur 
in this greenstone. The same is the case with the green- 
stone rock on which Stirling Castle is built. The only place 
where I saw a rock, which, on a general view, had some 
resemblance to your greenstones, was at Roffiat near to St 
Flous, where it occurred in the middle of a stream of basaltic 
lava. It seemed to be a distinct compound of felspar and au- 
gite, but was without crystals of olivine. 
5. I examined very carefully the different basaltic veins 
(whin-dikes,) that occur in the districts over which I travelled. 
Near Murat in the Cantal, I found a pretty broad basaltic 
vein running from top to bottom of a hill, composed of a vol- 
canic tuffa, including much porous lava, and capped with 
beautiful basalt pillars. The veins contain elongated cavities, 
some of which are entirely filled with calcareous spar and arrago- 
nite ? while others were only lined with small wax-yellow crys- 
tals, of a substance called Mellilite. At St J aques, at the foot 
of that porphyritic mass the Plomb du Cantal, I found a por- 
phyritic vein, running through a white-coloured volcanic tuf- 
fa. The vein was porphyritic basalt. It was partly amyg- 
daloidal, and many of the amygdaloidal cavities were lined 
with calcareous spar, others with a matter like green earth. 
It appeared to contain small grains of iron-pyrites and of augite. 
But I did not find any rock precisely similar in my collec- 
tion of Scotch specimens, notwithstanding many of your basal- 
tic veins are disposed, as is the case with this one, in small ho- 
