John Josias Conybeare

“ 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. ”

“ Having observed in the walls of the neighbourhood several specimens of those porphyritic and granitic rocks, which are distinguished in the country by the name of elvans, we were induced to enquire more particularly into their Geological relations, and the frequency of small promontories on the coast afforded us a favourable opportunity of ascertaining their position in several spots. ”

“ The lodes are principally worked for tin, though copper is occasionally raised. The prevailing rock is killas, and the nearest point at which granite has been noticed is in the Gwennap cluster of mines about six miles distant. ”