APPENDIX. 399 



by the quantity of alluvial matter it carries clown, and a search 

 for this organic fossil must prove unsuccessful. But during the 

 prevalence of the summer droughts, in an atmosphere of little 

 humidity, when the waters are drained to the lowest point of de- 

 pression, and acquire the greatest degree of transparency, it forms 

 a very conspicuous trait in the geology of the stream, and no per- 

 son, seeking the spot, can fail to be directed to it. 



The sand-rock containing this petrifaction is found in a hori- 

 zontal position, differing only with respect to hardness and color. 

 The remains of fossil organized bodies in this stratum are not 

 abundant, or have not been successfully sought. It is probable 

 that future observations will prove that its organic conservata 

 are chiefly referable to the vegetable kingdom. It is certain, that 

 this inference is justified by the facts which are before me, and 

 particularly by the characteristic appearances of the strata in the 

 bed of the River Des Plaines, where the imbedded walnut is the 

 representative of the ancient flora. At a short distance above, 

 where the bed of the Des Plaines approaches nearer the summit 

 level, limestone ensues, and continues from that point northward 

 to the shores of Lake Michigan. In the vicinity of Chicago, 

 where this limestone is quarried for economical purposes, it is 

 characterized by the fossil remains of molluscous species. 



Lake Erie lies at an elevation of five hundred and sixty-five 

 feet above the Atlantic.* 



There exists a water communication between the head of Lake 

 Michigan, at Chicago, and the River Des Plaines, during the 

 periodical rises of the latter, but its summer level is about seven 

 feet lower, at the termination of the Chicago portage, than the 

 surface of the lake. From this point to its junction with the 

 Kankakee, a computed distance of fifty miles, the bed of the Des 

 Plaines may be considered as having a mean southern depression 

 of ten inches per mile, so that the floetz rocks at its mouth, lying 

 on a level of forty-eight feet eight inches below the surface of 

 Lake Michigan, have an altitude which cannot vary far from five 

 hundred and fifty feet above the Atlantic. There are no mount- 

 ains for a vast distance either east or west of this stream. It is a 



* Public Documents relating to the New York Canals, with an Introduction, &c., 

 by Colonel Haines. 



