138 LOWER PENINSULA. 



of rock beds of the coal measures, where the erosions of the drift 

 period have not destroyed them and filled their place with debris. 

 The upper sand rock of the formation is in many places entirely 

 swept away, and the shale beds below lie denuded at the surface. 

 The two mines opened at Corunna, a mile or two east of the vil- 

 lage, have begun their shafts in the shale beds ; one of them, the 

 more northerly situated, was abandoned at the time of my visit ; 

 the other, located within a short semicircular bend of the river, 

 was worked. In the oblique drift leading to the bottom of the 

 mine, the following section is offered : 



Drift 9 ft. 



Shale, dark, partly black 30 " 



Sandstone , 4 " 



Black slaty shales, containing Lingula and Dis- 



cina, besides compressed Lamellibranches. . 6 " 



Coal I " 



Fire-clay 4 " 



Black slaty shales, as above 8 " 



Coal from 3 to 4 " 



Fire-clay 4 " 



Black shales 4 " 



Arenaceous shales continue to the bottom, which is 80 feet below 

 surface. The beds are found in the mine rising and sinking in un- 

 dulations. The fire-clay seams are usually arenaceous and contain 

 stems of Stigmaria. The shale beds contain lenticular concretions 

 of kidney ore, in the non-decomposed condition of gray, amorphous 

 carbonate of protoxide of iron ; seams and nodules of iron pyrites 

 are also found dispersed throughout the whole formation. In 

 the coal seam the pyrites are concentrated into a band of a few 

 inches in thickness. The coal is of bituminous quality, of the same 

 character as the Jackson coal. Not far off, west from the mine, the 

 shale formation is found covered by the upper coarse-grained sand 

 rock inclosing stems of Calamites. The visible thickness of the rock 

 is about 15 feet, but it is probably thicker if it could be seen better 

 exposed. Other outcrops of the sandstone are to be found in the 

 river bed 4 miles above Corunna. The coal measures are fre- 

 quently noticed in the bed of the Shiawassee below Owosso, as far 

 down as St. Charles. A locality of particular interest is near the 



