STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 29 



sible only on the eastern and western margins. The maximum 

 thickness of coal, as far as can be ascertained, is near the middle 

 of the eastern border, whence it thins toward the north and the 

 soath. The coal in all mines, of which Taylor gives measurements, 

 is near the base of the section and rests on the granite or is separated 

 from it by, at most, a few feet of shale. The overlying rocks, for 

 about 400 feet, as cut in shafts on both sides of the trough, are 

 mostly grits, sometimes conglomeratic, with interstratified gritty" 

 micaceous, carbonaceous or argillaceous shale. 



In the northeastern part of the trough, he saw two seams, 5 

 and 3 to 4 feet, separated by 10 or 12 feet of slate and about 10 

 feet from the granite, there being a thin seam in the latter interval. 

 On the northwestern side, the seams are 30 feet apart and are 6 to 

 16 and 4 to 8 feet thick. These are said to unite farther north. 

 The lower seam, of rather inferior quality, rests on the granite. 

 On the eastern border, the Chesterfield shaft shows (i) coal shale, 

 6 feet, 10 inches; (2) coal, 5 feet, 6 inches; (3) coal shale, 3 feet; 

 (4) coal, I foot, 6 inches ; (5) hard grits, 2 feet, 6 inches ; (6) shale 

 and thin coal, 2 feet, 6 inches; (7) coal, 7 to 40 feet; (8) granite. 

 The lowest coal has some variable partings. The sections on this 

 side of the trough are much alike ; but the coals, 4 and 6, are not 

 always present and not infrequently some shale was seen between 

 the coal and the granite. 



As the mines had been worked extensively prior to Taylor's 

 visit, he had opportunity to examine considerable spaces from which 

 the coal had been removed so that the underlying granite surface 

 was exposed. Not rarely a boss of granite rose through the lower 

 division of the seam; in such cases, the work was usually abandoned ; 

 but occasionally a drift was carried around the boss and entered 

 a body of coal, filling a hollow, 50 or 40 feet deep. There is no 

 parallelism between top and bottom of the seam. The roof is 

 irregular, rising and falling, and the depressions sometimes reach 

 the floor, but they never conform to the irregularities of the granite 

 surface. In spite of these irregularities, the lamination of the coal 

 is wholly undisturbed. The lower part of the seam is less clean 

 than the upper, but the coal is fat and coking throughout. 



Rogers was studying the region at the time of Taylor's visit. 



