388 



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 be 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 six 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 palaeozoic 

 or oldest mesozoic ages. But it has also been found in talcose-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 w^ould be likely to contain a 

 mcreuriferous gangue or matrix ; and, referring to the known erratic 

 origin of metalliferous deposits, there is no difficulty 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 



