Historic Diaries: James Doty, 1820
June 11, 1820: Schoolcraft, on Mackinac's Geology
Editor's Note:
Doty did not write in his diary this day, so we insert an entry from Schoolcraft's journal that shows him in his role of expedition geologist.
Schoolcraft continues at some length in a similar vein, which we assume is only interesting to the historian of geology. Readers who wish to read more can find the rest of his disquisition in chapter three of his book, online at the Library of Congress American Memory project.
Location: Mackinac Island, Mich.
The geological character of the island of Michilimackinac presents some features which, so far as observations have enabled us to judge, are peculiar to it.
"It consists of a stratum of limestone of immense thickness, based upon a calcareous rock, in which the semi-crystalline structure, and almost entire absence of fossil remains, prove its intermediate age. This formation is not elevated more than a foot above the level of the lake, and extends horizontally under the island. It is overlayed by the rock forming the bluffs which have so commanding an appearance on the approach to the island, and attaining various elevations from one hundred to three hundred feet. Its compact structure, and imbedded fossils leave no doubt as to its posterior deposition, but what strikes us as peculiar in this formation is the circumstances of its being made up of fragments of both transition, and compact limestone, with cavities of carbonat of lime in the powdery form, (agaric mineral) together with small fragments of a species of striped flinty agate, and innumerable small crystals of calcareous spar, thus giving it a breccioidal appearance…"
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