Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/413

 the drawing annexed. It has been much worked for tin, which is disseminated through its mass in veins apparently contemporaneous. The killas which is traversed and covered by these more crystalline rocks, has, for the most part, the characters usually ascribed to clay slate, and its strata occasionally present singular curvatures; in many places it passes into chlorite slate, and in the immediate neighbourhood of these dykes it usually presents either a highly crystalline form of that rock, or such an intermixture of it with quartz and felspar as might fairly be esteemed a variety of gneiss. This change of appearance has it is well known been attributed by the most able advocates of the Huttonian theory to the action of the injected mass, while yet in a state of fluidity. To us, the aspect of the rock at the point of contact did not, (either in this or any other instance of the same phenomenon, which fell under our notice), appear to be such as we could conceive to have resulted from that process.

We were in almost every instance strongly tempted to regard the elvans as of contemporaneous formation with the schistose rock which they traverse. We are conscious however that our observations were neither sufficiently accurate or extensive to warrant the advancing any thing like a decided opinion upon this curious subject.