888 
THE GEOLOGIST. 
beds near the intersections of the joints, of a soft whitish clay, or impure 
description of kaolin. The occurrence of the two last-named minerals 
in the granite, in the manner described, is nothing more than we should 
expect to find in an ordinary rock of the kind ; but, in connection with 
the presence of the arsenical pyrites, their occurrence is interesting, as 
indicating an aqueo-chemical origin, and pointing to changes having 
taken place, such as might bo favourable to the existence of, to use a 
mining phrase, a mineral-bearing condition of the ground. This view 
was supported by my being able to procure small specimens of cinnabar 
from three little strings (they were not of a magnitude to be called 
veins) of quartz, which ran south-west, and were traceable throughout 
the whole lateral breadth of the quarry, being, no doubt, continued 
under the adjoining covered rock. Small and insignificant as they were, 
the largest being less than sis inches wide, they possessed a regular 
vein-stone, and had many of the true characters common to mineral 
veins. 
As a rule, I believe metallic mercury is always associated with 
cinnabar, and its distribution is nearly confined to rocks of the palajozoic 
or olded mesozoic ages. But it has also been found. in tatcose-slate in 
Hungary, and, according to Dana, sparingly in granite ; and these, 
with the foregoing, are probably the only rocks in which either mercury 
or its ores ever really exists in situ, although it is quite possible that 
there may be localities where even the newest formations of the 
mesozoic age may have undergone such changes by contact with igneous 
rocks as to have become mineralised with this metal. Without, then, 
indulging, in consequence of the facts above related, in any vaticination 
for the discovery hereafter of important mines of mercury in the neigh- 
bourhood of Ajaccio, the presence of the cinnabar in the granite at that 
place, so near to the place where the metal was discovered in the soil, 
is interesting, because it at once suggests the origin of the deposit, and 
supplies a rock of such a character as would be likely to contain a 
mercuriferous gangue or matrix ; and, referring to the known erratic 
origin of metalliferous deposits, there is no difiiculty whatever, in the 
case in point, in accounting for the existence of the mercury in the 
alluvium on the supposition that, with the progress of chemical decom- 
positions in the granite, such as those which were concerned in the for- 
mation of the kaolin, a joint connected with that portion of the rock 
containing the metal, either in a regular vein or otherwise, may have 
