in Birch-hill Colliery^ ^55 



^reat 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 glimmer- 

 ing lustre from the intermixture of minute, shining, crystalline 

 laminse ; 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 amor- 

 phous hornblende : it is to be remarked however of this latter sub- 

 stance that it exhibits no appearance of crystalline laminse, 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 eifervescence ; and the stone assumes a greyish white 

 colour consisting almost wholly of crystalline laminae 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 lie§ 

 .above the greenstone, diifers but little from the common slaty clay 



