396 M. Kozet o« the Effects of Veins of Quarts. 



yards to the north of the village, on the new road to CharoUes, 

 we observe the limestone, containing Gryphea arcuata, di- 

 rectly covering the granite, and so connected with it, that 

 there results an insensible, but mechanical passage, from the 

 one to the other. The granite, ^in its upper portions, being 

 impregnated with limestone, effervesces with acids ; and the 

 limestone, in its inferior portions, contains so large a quantity 

 of crystals of felspar, that there results a very singular calci- 

 phyre. Near the bottom, the felspar is much more abundant 

 than the hmestone, but it diminishes as we proceed upwards, 

 and, at a yard and a-half above the granite, the crystals of 

 felspar have disappeared. In all this portion of the lias-for- 

 mation there is not a trace visible of organic remains. But 

 in the beds immediately above, and which are intimately con- 

 nected with the calciphyres, we find abundance of the Gryphea 

 arcuata and other characteristic fossils. In the portion contain- 

 ing the crystals of felspar, the stratification of the limestone is 

 very confused, and, indeed, frequently has entirely disappear- 

 ed ; the limestone itself is much altered ; its density is sensi- 

 bly augmented ; it has assumed a yellowish colour and a crys- 

 talline aspect ; at a greater distance it has become brown, with 

 yellow spots ; this last variety contains few crystals of felspar ; 

 in the two modified varieties we remark a great number of 

 quartz veins, which lose themselves insensibly, and never rise 

 to the shelly beds ; below, the veins become connected with 

 lai'ge trunks which traverse the inferior granite, and are true 

 veins, identical with those which we notice in the whole gra- 

 nitic mass. It is the eruption of the quartz, evidently contem- 

 poraneous with the first period of the lias deposit, which has 

 thrown the crystals of felspar into the limestone, and amalga- 

 mated with it the granite which had been cooled for a long 

 period previously. In all this portion the limestone has be- 

 come magnesian, and especially in the neighbourhood of the 

 veins of quartz. The brown variety, which is the most altered, 

 and in which the veins of quartz are the most numerous, is 

 also the most magnesian. I found in it nearly a third of mag- 

 nesia, of iron, and of silica, a fact which has been confirmed at 

 the School of Mines by M. Elie de Beaumont. 



Here, then, we have an example of limestones rendered 



