424 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



to 300 meters, is the most important coal-bearing portion. Of the 

 II seams reported in the section, 8 have a maximum of 0.7 to 1.75 

 meter inclusive of partings. Marine fossils were observed in the 

 roof of 5 seams. 



Cg, about 2,000 meters thick, contains workable coal only in the 

 lower horizons. The fauna changes gradually ; forms of the middle 

 division disappear and new forms appear, which are characteristic 

 of the Upper Carboniferous in Timan and in North America. The 

 lowest subdivision has 10 seams, but all are thin and the coal is poor. 

 In one case, the roof contains marine fossils. Red to green shales 

 are in the upper part of the section. The second is separated from 

 the first subdivision by 1 1 meters of marine limestone and contains 

 2 or 3 coal seams, which are wholly unimportant. Arkose near the 

 base has fragments of Araucaria and the section shows some green 

 and red shale. The third subdivision has only thin streaks of coal 

 and thin beds of red shale. The fauna and the flora are distinctly 

 Upper Carboniferous. 



The number of coal seams, which, at some place, attain workable 

 thickness, is not more than 30; but the variability both in thickness 

 and in quality is extreme ; some disappear, others become thin and 

 worthless while new ones appear. The coal loses volatile in the 

 direction of increasing dip. At mines in the Almazny seam, along 

 a northwest-southeast line, only 20 miles long, the volatile is 35, 30, 

 25, 18, 15 or less per cent. The proportion of volatile has no rela- 

 tion to nature of the roof or floor. The authors regard the Donetz 

 coals as allochthonous, the convincing argument being the presence 

 of marine fossils in the immediate roof of coal seams. 



Permo-Carboniferous deposits are confined to the western side 

 of the Donetz Basin, where they rest directly on the limestone 

 closing-Cg. Deposition was continuous from Carboniferous to Per- 

 mian and there is no evidence of unconformity anywhere. The 

 deposits are regarded as Lower Permian and the abundant marine 

 fossils are in greatest part forms characterizing the C3, the Upper 

 Carboniferous ; the change in fauna is as gradual as that in passing 

 from Co to C3. The lower portion consists of clayey shales and 

 gray, green or red limestones with some streaks of coal near the 

 base. The upper portion consists mostly of red and green marls 



