Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/263

 great fault (which was then first discovered) the miners found themselves unexpectedly in the upper bed of the third coal (i.e. the blind coal), and in this they continued to drive forwards the heading to pit B, a distance of about 100 yards.

I now proceed to a more particular description of the trap and of the adjacent beds.

The colour of the trap is a dark bluish green; it has a glimmering lustre from the intermixture of minute, shining, crystalline laminæ; its fracture is uneven, and it breaks into irregular wedge shaped blunt edged fragments; it is tough, acquiring a kind of polish under the hammer, moderately hard and rather heavy. It attracts very strongly the magnetic needle, but does not exhibit any signs of polarity: it effervesces moderately on being immersed in cold dilute muriatic acid, and on examination with a lens appears to consist of felspar, of calcareous spar, of minute shining black grains, and of a brownish, blackish, and bluish green substance, which I suppose would generally be considered as amorphous hornblende: it is to be remarked however of this latter substance that it exhibits no appearance of crystalline laminæ, and that if a piece of the entire rock be digested in boiling dilute nitro-muriatic acid this green matter is almost entirely dissolved with considerable effervescence; and the stone assumes a greyish white colour consisting almost wholly of crystalline laminæ of felspar.

This trap or greenstone is penetrated by contemporaneous nearly vertical veins of calcareous spar, from the size of a mere thread to about half an inch in thickness. The rock, although very compact in its recent state, after a few weeks exposure to the air, acquires a liver-brown colour and crumbles to pieces.

The slaty clay, with subordinate beds of ironstone, which lies above the greenstone, differs but little from the common slaty clay