398 APPENDIX. 



Illinois, as well as to most other parts of the immense region 

 drained by the waters of the Mississippi. The woody structure 

 is most obvious in the outer rind of the trunk, extending to a 

 depth of two or three inches, and these appearances become less 

 evident as we approximate the heart. Indeed, the traces of or- 

 ganic structure in its interior, particularly when viewed in the 

 hand specimen, are almost totally obliterated and exchanged, the 

 vegetable matter being replaced by a mixed substance, analogous, 

 in its external character, to some of the silicated and impure cal- 

 careous carbonates of the region. Like those carbonates, it is of 

 a brownish-gray color and compact texture, effervesces slightly 

 in the nitric and muriatic acids, yields a white streak under the 

 knife, and presents solitary points, or facets, of crystals resembling 

 calc spar. All parts of the tree are penetrated by pyrites of iron 

 of a brass yellow color, disseminated through the most solid and 

 stony parts of the interior, filling interstices in the outer rind, or 

 investing its capillary pores. There are also the appearances of 

 rents or seams between the fibres of the wood, caused by its own 

 shrinkage, which are now filled with a carbonate of lime, of a 

 white color and crystallized. 



From an effect analogous to carbonization, the exterior rind 

 and bark of the tree have acquired a blackish -hue, while the in- 

 closing rock is of a light-gray color, characters which are calcu- 

 lated to arrest attention. 



There is reason to conclude that the subject under considera- 

 tion is the joint result, partly of the infiltration of mineral matter 

 into its pores and crevices, prior to inclosure in the rock, and 

 partly to the chemical action educed by the great catastrophe by 

 which it was translated from its parent forest, and suddenly en- 

 veloped in a bed of solidifying sand. 



At the time of my visit (August 13, 1821), the depth of water 

 upon the floetz rocks forming the bed of the Eiver Des Plaines, 

 would vary from one to two feet ; but it was at a season when 

 these higher tributaries, and the Illinois itself, are generally at 

 their lowest stage. Like most of the confluent rivers of the Mis- 

 sissippi and their tributaries, the Des Plaines is subject to great 

 fluctuations, and during its periodical floods may be estimated to 

 carry a depth of eight or ten feet of water to the junction of the 

 Kankakee. At those periods, the water is also rendered turbid 



