A memoir on the geological position of a fossil tree, discovered in the secondary rocks of the river Des Plaines. Read before the American Geological Society.

  • Henry Schoolcraft
Date:
1822
Catalogue details

Licence: Public Domain Mark

Credit: A memoir on the geological position of a fossil tree, discovered in the secondary rocks of the river Des Plaines. Read before the American Geological Society. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    On floetz sandstone. This formation, which constitutes the north- eastern angle of the state of Illinois, where the waters of Michigan lake and the Illinois river often approach within a few miles of each other, and actually communicate at Chicago, continues east, and northeast, spreading in its course through Indiana into Ohio, and embracing the entire peninsula of Michigan. It is covered with a deposit of alluvial soil of a productive character, and pre- sents to the eye a series of level prairies, interspersed with occa- sional forests, and irrigated by numerous small lakes and streams. These features may be considered as peculiarly characteristic of the district of country drained by the rivers Kankakee and Des Plaines, which uniting their channels at the distance of forty miles south of Chicago, produce the Illinois. The junction is effected on the southern slope of table land which confines lake Michigan to the north, at a point where the waters descend with considera- ble velocity, over a horizontal layer of shelving rock, which pro- duces a series of rapids, and is continually yielding to the action of the water ; but there is nothing in the mineral physiognomy of the spot so remarkable as the petrified tree, which is found in the bed of the river Des Plaines about forty rods above its junction with the Kankakee. This extraordinary species of pnytolites occurs imbedded in a horizontal position in a stratum of newer floetz sandstone, of a grey colour, and close grain. There is now fifty-one feet, six inches of the trunk visible. It is eighteen inches in diameter at the smallest end, which appears to have been violently broken off, prior to the era of its mineralization. The root-end is still over- layed by the rock and earth in the western bank of the river, and is two feet, six inches in diameter at the point of disappear- ance ; but circumstances Will justify the conclusion that its diam- eter at the concealed end, cannot be less than three feet. The trunk is straight, simple, scabrous, without branches, and has the gradual longitudinal taper observed in the living specimen. It lies nearly at right angles to the course of the river, pointing towards the south-east, and extends about half the width of the stream. Notwithstanding the continual abrasion to which it is exposed by the volume of passing water, it has suffered little ap- parent diminution, and is still firmly imbedded in the rock, with the exception of two or three places where portions of it have been disengaged, and carried away ; but no portion of what re* mains is elevated more than a few inches above the surface of
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