Dr Daubeny on the Ancient Volcanoes of Auvergne. 605 
the torrents, could be brought by the torrents, could be fully 
explored, the beds of tuff which are there met with might be 
found to contain it. 
The following is the result of Cordier’s analysis, together 
with that of the Tolfa aluminite by Klaproth and Vauquelin ; 
the former at least has never, I believe, found its way into any 
English scientific Journal. 
Alumstone of Tolfa. 
Alumstone of Mont (VOr. 
Alumine, 
Vauquelin. 
» 43.92 
Klaproth. 
19.50 
Alumine, 
Cordier, 
31.80 
Silex, 
24.00 
56.50 
Silex, 
28.40 
Potash, 
- 3.08 
4.00 
Potash, 
5.79 
Sulphuric acid, 
25.00 
16.50 
Sulphuric acid, 
27.05 
Water, - 
. 4.00 
3.00 
Water, 
3.72 
Loss, 
- 0.00 
1.00 
Protoxide of Iron, - 
- 1.44 
100.00 
100.00 
Loss, 
1.80 
100.00 
Near the village of the Baths, the trachyte is traversed by 
several dikes of vesicular lava, which are connected above with 
the basaltic formation. They occur in a deep ravine, which ap- 
pears to have been made in the side of the valley wherein the 
Baths are situated, by a waterfall, which is commonly called 
the Grande Cascade de Mont d’Or,” although at the time I 
visited it, its magnitude did not seem to entitle it to that dis- 
tinction. Of these dikes, some might be supposed to have been 
forced up from below, since their terminations are not visible, 
but two others were distinctly seen ending in the trachyte. It 
might be said, indeed, that the apparent termination of the 
dikes in this instance proves nothing, as it is possible the vein 
might have been continued in that portion of the rock which 
has been removed by the excavation- of the valley ; and though 
the vertical direction of the vein, with no apparent inclination out- 
wards, does not favour that idea, I might nevertheless have admit- 
ted it, had there been any evidence of dislocation or hardening in 
the rock which is traversed by it. The absence, however, of any 
alteration that I perceived, either in the position or in the ex- 
ternal characters of that portion of the trachyte which lies con- 
tiguous to the veins, leads me to suppose that the latter has 
been formed from above out of the basaltic lava, which might 
have insinuated itself, while in a liquid state, into cracks or 
VOL. IV. NO. 8. APRIL 1821. 
u 
