imth those of a similar Nature found in Scotland, 3^9 
rizontal columns. Near to the top of the part which unites 
the Col de Cabra with the Puy Marie, I had the pleasure of 
observing three fine basaltic veins, traversing a pretty porous 
trachyte or volcanic porphyry. The porphyry is of a red 
colour, and contained numerous small crystals of glassy felspar. 
The middle vein is about one foot and a half broad, and is 
composed of a very black, compact, dull, heavy basalt, inclos- 
ing grains of olivine, and perhaps also of augite. The vein to 
the west of this is one foot wide, and the third to the east three 
feet ; and between this last and the middle one, there is still ano- 
ther, about half a foot wide. . Not far from these veins there 
are vertical sections of streams of basaltic-lava, which rest up- 
on immense inchned beds of various kinds of volcanic tuffa, 
in which there are occasionally found masses of basalt, bearing a 
great likeness to that which forms the veins. But one of the 
most interesting of these veins I examined, was observed at 
Villeneuve Le Berg, traversing limestone. The basalt has 
nearly the same characters as that of St J acques ; it contains 
many crystals of augite, and is sometimes amygdaloidal, and the 
cavities are filled with calcareous spar, or lined with iron-pyri- 
tes. The limestone, where in contact with it, is rendered more 
compact ; and the same is the case with the numerous pieces of 
limestone contained in the vein, particularly towards its crop or 
outgoing. But in no instance is the limestone crystallised or 
changed into marble ; all I could observe was a simple harden- 
ing of a rather earthy looking limestone. I examined the cow- 
tact-limestoney with the view of ascertaining if in any case it 
would not effervesce with acids, but I found all the varieties, 
even the most compact, effervesced with acids. In favour of 
what theory is this fact ? I dare not adopt the filling up from 
above, it is attended with so many difficulties ; but the volcanic 
hypothesis of injection into a rent is somewhat countenanced by 
the great accumulation of fragments towards the crop of the 
vein ; its mode of termination near the surface, and several 
other circumstances. 
6. On visiting Auvergne, I expected to obtain some satisfac- 
tory ideas in regard to your Scottish pitchstones, particular- 
ly those of the Island of Arran, but have returned with only a 
single fact, viz. that veins which are partly of basalt, partly of 
VOL. II. NO. 4. APllTL 1820i 
Y 
