g. Strontian Minerals.
Sulphate of Strontian.
Foliated Sulphate of Strontian.—At Presque Isle (Wayne's Battle Ground), on the Maumee River, Wood County, Ohio. It occurs in veins and cavities, in compact limestone, most commonly in the form of flattened prisms. Its color is blue, frequently a very light or sky-blue, and the crystals are fully translucent, or even 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 River, 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 scattered 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 River 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 observed, in situ, is at La Charbonniére, 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 visit; but the nature and position of the rock strata and soils, and the general aspect of the country, do not justify the conclusion that the bed is of much thickness or extent. Valuable beds may be discovered, however, by exploring this formation. This coal has a shining black color, a slaty structure, inflames readily, burning with a bright flame. It is very fragile where exposed to the weather, falling into fine fragments. Hence, a very black color has been communicated to the contiguous and overlaying soil, which is manifestly more or less the result of disintegrated coal.
Detached fragments of coal, corresponding in mineral characters with the above, are occasionally found around the southern shores of Lake Michigan. The inference, as to the existence of coal around the shores of this lake, is obvious. And we are led to inquire: Does the La Charbonniére formation of coal exist in the sandstone and limestone strata forming the table-land between the Illinois River and Lake Michigan, and reappearing around the basin of the latter, but at such a depression below its surface as to elude observation? And, if so, does not this coal formation extend quite across the southern portion of the peninsula of Michigan? The secondary character of the region alluded to, so far as observed, the horizontal and relative position of the strata, and the general uniformity which is generally observed in the species and order of the coal measures, favor this suggestion.
i. Soda.
1. Muriate of Soda.