358 APPENDIX. 



transparent. In some instances, they appear to have suffered a 

 partial decomposition, and fall into fragments in the act of raising, 

 or are covered with a white powdery crust, frequently visible 

 only on the summits or terminating points of the prisms. The 

 same limestone yields crystallized calcareous spar. Both these 

 substances are abundant in the rocky banks and in the bed of 

 the Maumee. Also, on Grosse Isle, Detroit Eiver, Michigan. 



h. Bituminous Minerals. 



1. Bitumen. 



Petroleum. — Occurs in cavities, in loose fragments of limestone 

 rock, along the west shore of Lake Michigan, between Milwaukie 

 and Chicago. These masses of rock lie promiscuously among 

 fragments of quartz, granite, sandstone, fossil madrepores, &c., 

 along the alluvial shore of the lake, and appear to have been 

 washed up from its bed. The petroleum is in a free and liquid 

 state; but, where it has suffered an exposure to the atmosphere, 

 it has acquired a stiff and tar-like consistence passing into maltha. 

 Not unfrequently, fragments of mineral coal are also found scat- 

 tered along these shores, and there is reason to conclude that a 

 bituminous formation exists in the contiguous inferior strata 

 forming the basin of the lake. 



2. Graphite. 



Granular Graphite. — In a small vein, in the clay-slate of the 

 Eiver St. Louis, at the head of the nine-mile portage. It is 

 coarse-grained and gritty. 



3. Coal. 



Slaty Coal. — The only spot where this mineral has been ob- 

 served, in situ, is at La Charbonni^re, on the west banks of the 

 Illinois River, at the computed distance of one hundred and 

 twenty miles south of the post of Chicago. It is here seen in 

 horizontal strata, not exceeding two or three inches in thickness, 

 interposed between layers of sandstone and shale. Breaking out 

 on the declivity of the bank of the river, where the overlaying 

 strata are constantly crumbling down, and thus obscuring the 

 seams, no very satisfactory examination could be made in a hasty 



