COAL MEASURES. 1 37 



and black slate and lighter shales to the depth of 60 feet in all 

 below the surface. 



The above experiments show a uniform distribution of a coal 

 seam about 3 feet in thickness over this whole district. Its position 

 is often too superficial, without a proper roof, for advantageous 

 mining. In nearly all the borings two seams of coal are found, of 

 which the upper one is generally too narrow to be of practical 

 value. The two seams are separated by from 15 to 20 feet of in- 

 termediate beds. 



The next disclosures of the coal measures we find on Shiawassee 

 River, near Owosso, and Corunna, in both of which places coal mines 

 • are opened. The shaft of the Owosso mine is close to the river, within 

 the village limits. It begins in a blue shale with coaly, vegetable re- 

 mains, under which a coal bed of 15 inches is found resting on fire- 

 clay 6 feet in thickness; then another coal seam, likewise of 15 

 inches, succeeds. The bottom part of the shaft, which is 40 feet 

 deep, is formed by shales and fire-clay ; the fire-clay is partly of a 

 hard, sandy nature, and contains numerous stems and leaves of 

 Stigmaria ficoides. The coal is of a rich bituminous quality and 

 tolerably free of sulphur, but the seams are too thin to be profit- 

 ably mined. Several companies tried to work it, but gave it up 

 after a short time, as not returning enough to cover the expense. 



At the Detroit and Milwaukee Railroad depot, a boring to the 

 depth of 307 feet has been executed. Its record runs : 



Drift 40 ft. 



Fire-clay 5 " 



Blue shale 20 " 



White arenaceous shale 8 " 



Blue shales, partly arenaceous 107 " 



Coal 6 in. 



White sandstone 16 ft. 



Shales 22 '^ 



Blue sand rock, alternating with shale 46 " 



White sand rock 11 '' 



Dark shale 5 " 



Sand rock 2"/ '' 



Shales to the bottom of the boring. 



The bottom of the Shiawassee valley, near Corunna, is all formed 



