Ch. IV.] SCHISTOSE GROUP OF CORNWALL. 53 gular crystals of felspar may be observed here and there, but they are of rare occurrence : its junction with the slate is not exposed. At Kernick, about three miles from Bodmin, there are several beds of granitic rocks: the mica is in larger scales than in the last, and 'small portions of hornblende are dis tinctly developed; and here also their junction with the slate on either side is concealed, so that their size and bearings cannot be ascertained. About a mile and a half from Bodmin, on the road to Truro, an interesting kind of eurite occurs, which we have termed porcelainous eurite, as indicating its nature. It is of a pale greenish yellow colour, rather uniform and compact, but containing grains of limpid quartz : it decomposes to a considerable extent, and then resembles china-clay, which has been already described as a disintegrated protogine, a rock distinguished from granite by containing talc instead of mica, and which abounds in the mass of granite about three miles off. If this bed of porcelainous eurite were well ex posed, its constituent minerals would probably be distinctly exhibited, as is generally the case in the middle of these elvan-courses, where the rock becomes porphyritic and even granitic. Granular and compact shorl rocks also occur in this part of Cornwall imbedded in proteolite, and although at first sight these rocks appear to have a very dissimilar composition, yet a careful examination will show that they are nearly related. The proteolite is frequently coloured by or even intermixed with shorl, in various states ; and when the compact felspar basis becomes siliceous, the shorl is present in greater abundance, till at last it graduates into compact shorl-rock, and the constituents becoming distinctly crystallised, the granular shorl-rock is produced. The celebrated Roach rock is composed of the last-mentioned variety : it rises out of the slate in the form of an immense tor, about a mile distant from the granite.