APPENDIX. 897 



at the source of the Illinois River, Having recently visited this 

 evidence of former changes in the flora of the West, I embrace 

 the occasion, while my recollections are fresh, to give an account 

 of it. 



The tract of country separating the southern shores of Lake 

 Michigan from the Illinois River, is a plat of table-land composed 

 of compact limestone, based on floetz or horizontal sandstone. 

 This formation embraces the contiguous parts of Illinois, and 

 spreads through Indiana, Ohio, and the Peninsula of Michigan. 

 If is overspread with a deposit of the drift era, covered with a 

 stratum of alluvial soil, presenting a pleasing surface of prairies, 

 forests, and streams. These features may be considered as pecu- 

 liarly characteristic of the junction of the Rivers Kankakee and 

 Des Plaines, which constitute the Illinois River. This junction 

 is effected about forty miles south of Chicago. 



The fossil in question Occurs about forty rods above the junc- 

 tion of the Kankakee. The sandstone embracing it is deposited 

 in perfectly horizontal layers, of a gray color and close grain. It 

 lies in the bed of the Des Plaines. The action of this stream has 

 laid bare the trunk of the tree to the extent of fifty-one feet six 

 inches. The part at the point where it is overlaid in the western 

 bank is two feet six inches in diameter. Its mineralization is 

 complete. The trunk is simple, straight, scabrous, without 

 branches, and has the usual taper observed in the living speci- 

 men. It lies nearly at right angles to the course of the river, 

 pointing towards the southeast, and extends about half the w.idth 

 of the stream. Notwithstanding the continual abrasion to which 

 it is exposed by the volume of passing water, it has suffered little 

 apparent 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 

 remains is elevated more than a few inches above the surface of 

 the rock. It is owing, however, to those partial disturbances 

 that we are enabled to perceive the columnar form of the trunk, 

 its cortical layers, the bark by which it is enveloped, and the 

 peculiar cross fracture, which unite to render the evidence of its 

 ligneous origin so striking and complete. From these characters 

 and appearances, little doubt can remain that it is referable to the 

 species juglans nigra, a tree very common to the forest of the 



