Dr Daubeny on tlie Ancient Volcanoes (^Auvergne. 801 
These are the rocks which appear to me to supply the con- 
necting link between what is called the Newest Floetz-Trap For- 
mation of Werner, and the products of existing volcanoes ; for 
those who have taken the trouble of perusing my former letter, 
will perceive that the rocks therein described differ in so many 
important points from the former, that we should hardly be jus- 
tified in arguing from the one to the other. Should it, however, 
appear that there is reason for concluding the chain of Mount 
d’Or to be of volcanic origin, I know not how we can help ex- 
tending the same inferences to many of the basalts of our own 
and other countries, to which it seems to present such striking 
and numerous analogies. 
Two classes of volcanic rocks compose the chain of Mount 
d’Or. On the summit of the great Table Land of which it 
consists, is a basaltic formation, associated with a sort of trap 
tuff or breccia and other rocks. 
Underneath this is a porphyritic felspar-rock seen exposed in 
the valleys, which has generally obtained the name of Tra^- 
chyte. 
Below all is seen the granite, which seems to constitute the 
original substratum throughout the whole of this Province ; 
the volcanic, and even the fresh water formation, hardly deser- 
ving to be considered as parts of the crust of the earth, but be- 
ing rather in some sense extraneous to its composition f* 
We shall consider these rocks in succession, beginning with 
the highest in the series. 
1. The Basaltic Formation of Mont d’Or comprises several 
rocks, differing from each ether much in appearance and exter- 
nal characters. 
The rock which has induced me to give this name to the 
whole, is a compact and sonorous basalt, generally containing 
* Although in general very averse to alterations in nomenclature, I cannot help 
agreeing with Dr MacCulloch in the propriety of substituting the term “ Trap- 
Breccia” for Trap-tuff, as the latter word is objectionable, not merely as inexpres- 
sive of the true character of the rock, but as conveying an erroneous idea of it. 
' -f M. d’Aubuisson, in his late work on Geognosy, not unaptly compares the 
Primitive Rocks to the skeleton of an animal, the Secondary to the muscular 
parts, and the Volcanic to the parasitical animals that are produced upon its sur- 
face. 
