Mesozoic and C'cenuzoic Geology and Palceontology. 11 



ly overlj'ing. One or two species of shells (Posidouomya?) also occur 

 in the same part of the series, at a small height above the coal-seams, 

 and above these a great number of fossil fish, chiefly referable to two 

 nearly allied species of a geaus, very distinct from any ichthyolite 

 hitherto discovered elsewhere. Above these fossiliferous beds, which 

 probably never exceed 400 or 500 feet in thickness, a great succes- 

 sion of grits, sandstone and shales of unknown depth occur. They 

 have yielded no coal, nor as yet any organic remains, and no specula- 

 tor has been bold enough to sink a shaft thi'ough them, as it is feared 

 that toward the central parts of the basin they might have to pass 

 through 2000 or 2500 feet of sterile measures before reaching the 

 fundamental coal seams. 



The coal is separated almost everywhere into three distinct beds, and 

 sometimes into five. The upper bed is the thickest, except in a few 

 places where a thin layer of coal is found above it. In some 

 places the main seam of coal is from 30 to 40 feet thick, and at Black- 

 heath it is seen actually to touch the fundamental granite, or is parted 

 from it only by an inch or two of shale. 



A section at the Midlothian Pit, half a mile south of Blackheath, on 

 the eastern outcrop of the coal, is as follows: Sandstone and shale, 

 570 feet; slate with calamites, 1^ feet; sandstone and shale, 43 10.12 

 feet; sandstone with calamites, 8 feet; sandstone and slaty shale, 48 

 feet; slate and long vegetable stems, 2^ feet; sandstone, 6|- feet; slate 

 with calamites, 5|- feet; sandstone, 14 feet; black rock, 13 feet; slate, 

 5 feet; main coal, 36 feet; sandstone not laminated, 5 feet; slate, 4 

 feet; coal, 1 foot; slate, 3 feet; sandstone or grit, 7 feet. Total, 773 

 10-12 feet. This rests upon granite of unknown depth. Some deduc- 

 tions must be made for the thickness of the beds on account of the in- 

 clination at an angle of 20 degrees. 



The unevenness of the granite floor is extremely great, and the thick- 

 ness of the coal seams quite variable. The disturbances have been 

 extremely great, and dikes of greenstone occur in some places 20 feet in 

 thickness. Some of the upper beds of coal have been reduced to coke, 

 by being deprived of their volatile matter, while others below remain 

 unaltered and bituminous. This is accounted for on the ground that 

 the greenstone, although intrusive, has made its way between the 

 strata like a conformable deposit, and has driven the gaseous matter 

 from the upper coal, while its influence has not extended to lower 

 seams. A remarkable example of coke, in a bed eight feet in thick- 

 ness, occurs at Edge-hill, a locality between five and six miles north 

 of James river, and ten miles north of Blackheath, being on the 



