Dr Daubeny on the Ancient Volcanoes of Auvergne. SOS 
referable to any law in the original formation of the rocks of 
which it forms a part, since we now and then meet with it un^ 
derneath other rocks 
From the description we have given, it will be easily under-^ 
stood, that the subjacent rock, the trachyto, is only seen expo- 
sed on the sides and in the bottom of the valleys, the great and 
elevated Table Land, which composes the range of Mont d’Or, 
and extends with little interruption into Cantal, having its up- 
per strata composed of basalt, and the other rocks associated 
with it; ,the scorified matter appearing to diminish in quantity, 
in proportion as we recede from the loftiest part of the chains 
That these strata are all volcanic, is pretty convincingly proved 
by the vesicular structure of those which lie uppermost ; for it 
seems impossible to assign a different origin to the basalt, and to 
the scorified matter superimposed ^ ; yet it is difficult to fonn 
an opinion in what direction this immense stream of lava can 
have flown, or from what point it could have been ejected. ' I 
noticed, indeed, one or two lakes, which gave me much the idea 
of their having once been craters, the Lake Servieres in parti- 
cular, to the north of the village of Les Bains, the sides of 
which are composed like the Puy Pariou, near Clermont, of 
•vesicular lava, and its form equally round and regular. Near it 
is a little hillock, not exceeding 50 feet in height, of a conical 
shape, consisting chiefly of the same materials. 
Yet, if this was a crater, the situation of the country must 
have greatly altered since the period at which it was in activity, 
its height, although absolutely great, being relatively to that of 
the rocks surrounding it, very inconsiderable. It lies, indeed, 
in the midst of this great Table Land, if it may be so termed, 
little, if at all, elevated above the general level. 
S. The Trachytic Formation Is essentially composed of crys- 
tals of glassy felspar, imbedded in a base of the same materials. 
Its fracture is more commonly rough and earthy, but is not un- 
frequently compact. In the latter state it is, that augite, mica, 
• As in the Isle of Lamlash underneath sandstone. 
•f M. d’Aubuisson has remarked at Pradelles, near Clermont, basalt incumbent 
on a bed of scoria. 
