in Birch Hill Colliery. 25*7 



from the Culm of South Wales, or the blind coal of Kilkenny ; 

 but where this coal is aot covered by the greenstone, it exhibits 

 the usual characters of common bituminous stone coal. 



The beds below this coal differ in no material respect from 

 similar beds in other collieries. 



Hence it appears that the Birch-hill colliery presents the follow- 

 ing important facts : First, the existence of a bed of greenstone 

 interposed between the usual strata of the coal formation, but not 

 co-extensive with them ; and secondly, that the coal and bitumi- 

 nous shale, where they are covered by the greenstone but protected 

 from actual contact with it by an indurated sandstone a yard in 

 thickness, differ materially in many respects, but chiefly in being 

 deprived of bitumen, from those parts of the same beds where 

 they are not covered by the greenstone. The works have not in- 

 deed been sufficiently opened to demonstrate that the changes just 

 mentioned are strictly co-extensive with the greenstone, yet I think 

 we may infer by fair analogy that such is the case ; and that the 

 greenstone is necessarily concerned in bringing about these changes. 



Professor Jameson, in his mineralogical account of Dumfries- 

 shire, mentions beds of greenstone occurring in the independent 

 coal formation ; and I at first took for granted, that the greenstone 

 above described was also a true bed. On further consideration, 

 however, I am rather inclined to adopt a contrary opinion, for the 

 following reasons ; 



In the first place the green rock fault being composed of pre- 

 cisely the same kind of greenstone as the bed is, renders it probable 

 that the one is a continuation of the other ; and this is still further 

 confirmed by the gradual thinning out of this bed as it recedes from 

 the fault ; for in the pit B, the most distant one that has been as 

 yet sunk through the gieenstone, this bed is 12 feet thick, while In 



Vol. hi, 2 k 



