Summary Narrative of an Exploratory Expedition to the Sources of the Mississippi River, in 1820 / Resumed and Completed, by the Discovery of its Origin in Itasca Lake, in 1832

by Henry Rowe Schoolcraft

2. Chlorite.

Chlorite Slate.—In subordinate strata in the argillite of the River St. Louis.

3. Staurotide.

In garnet-colored crystals, in detached blocks of mica-slate, in the drift of Lake Huron. These crystals consist of two intersecting six-sided prisms, truncated at both ends, forming the cross. They are nearly opaque, or feebly translucent on the fractured edge.

4. Clay.

1. Plastic Clay.—Very extensive beds of this clay are seen along the west shore of Lake Michigan, between Sturgeon Bay Portage and Chicago. Its color is generally a light blue, verging sometimes into deep blue or grayish-white. It is plastic in water, adheres strongly to the tongue, takes a polish from the nail, and emits an argillaceous odor when moistened or breathed upon. These beds of clay frequently contain iron pyrites, both in the crystallized and amorphous state.

2. Pipe Clay.—In the flats of the St. Clair and Lake George, Michigan. A bed of clay, apparently answering to this description, exists at White River, Lake Michigan. Its color is a grayish-white, verging to blue. It is very unctuous and adhesive when first raised, but acquires more or less of a meagre feel as it parts with its moisture, drying in firm and compact masses.

3. Variegated Clay.—On the banks of the River St. Peter's, Upper Mississippi. Neither the quantity in which it exists, nor the precise locality is known. Its color is white, variegated with stripes, spots, or clouds of red or yellow.

4. Azure Blue Clay of St. Peter's.—The locality of this substance, as communicated by the Indians, is the declivity of a hill, in the rear of the village of Sessitongs, one mile above the confluence of the Terre Blue River with the St. Peter's. It is found near the foot of this hill, between two layers of sandstone rock, in a vein about fifteen inches in thickness. This vein is elevated about twenty feet above the waters of the Terre Bleu, and does not extend far in the direction of the river. Having been resorted to by the Sioux Indians a long time, a considerable excavation has been made, but the supply is constant. The color of this mineral substance (its distinguishing character) is an azure copper blue of more or less intensity. It is ductile and moderately adhesive, when first taken up, or when moistened with water, but acquires an almost stony solidity on drying. It is considerably adulterated with sand or particles of quartz. It parts with its moisture rapidly on exposure to the atmosphere, and dries without much apparent diminution of volume.