Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/363

 Withycombe farm and Countesbury to Linton, and from thence through the Valley of Rocks by Slattenslade, Trentishoe, Combe Martin and Berry Narbor to Ilfracombe. A very great part of this country is entirely concealed by vegetation, but wherever the rock is exposed I found some variety of the grauwacke formation identical with those I had left behind. In that part of the road which is eastward of Linton, the coarser grained varieties are most frequent, but westward of that place the slaty varieties predominate, very often resembling some kinds of iron-grey clay-slate found in primary countries. Towards Ilfracombe this appearance becomes still more decided, and in a cabinet specimen it would be impossible to tell the difference. But beds of limestone with very decided indications of organic remains contained in this slate, show that it is of secondary formation, and at the same time afford a useful lesson of the inadequacy of mineralogical characters alone to determine the geological nature of a rock. These limestone beds are found between Berry Narbor and Hele; their resemblance to those I have described in the former part of this paper both in internal composition and in the accompanying slate, leave no doubt of their belonging to the same class. When struck with a hammer it emits a slight bituminous smell, a circumstance which I did not observe in the limestone of the other places I have mentioned, and it is traversed by very large veins of a transparent and very beautiful calcareous spar.

§ 20. Throughout the whole district described in this paper I found the grauwacke formation surrounded either by a conglomerate, or by a red sandstone, sometimes tolerably compact, but more frequently of a friable texture. These conglomerates and sandstones assume very various appearances, but under every form of aggregation the same materials may be traced. Where the