APPENDIX. 403 



kindly climates occupied by the secondary series. The soft and 

 decomposable nature of these depositions would furnish the true 

 theatre of vegetable life, and, until these regions were filled with 

 vegetables, the race of animals could not have been produced ; for 

 on what could they subsist? Graminivorous animals, therefore, 

 must have succeeded the various forms of vegetable existence ; 

 and carnivorous, the graminivorous. The vegetable matter im- 

 bedded in the substance of the secondary strata will consist of 

 the remains of vegetables that grow in the transition strata; and 

 the animal remains will consist chiefly of such animals as were 

 produced in the early stages of animal existence, particularly the 

 smaller aquatic animals; and, of these, chiefly shell-fish, as shells 

 are not so soon decomposed as mere animal substance." 



It is to the latter class of depositions — to the secondary series — 

 that we must refer the sandstone of the Kiver Des Plaines, in 

 which we find a walnut, of mature growth, enveloped by, and 

 imbedded in the rock, in the most complete state of mineraliza- 

 tion ; and, since all geological writers who subscribe to the Nep- 

 tunian theory are constrained to employ the agency of oceanic 

 depositions of different eras, in explaining the structure of the 

 earth's surface, it is one of the most obvious and important con- 

 clusions, to be drawn from the fact that such submersions and 

 depositions of rock matter have taken place subsequent to the 

 existence of forests of mature growth, and that the rock strata 

 and beds composing the exterior of the earth are the result of 

 different geological epochs, and of successive subsidences of chaotic 

 matter — positions which have been so severely attacked and so 

 often denied, particularly by the disciples of the Huttonian 

 school, that it is not without a feeling of lively interest, I com- 

 municate a discovery which appears so conclusive on the subject. 



Considerations arising from the frontier position of the country, 

 and the infrequency of the communication, have also induced me 

 to draw from incidental sources, a corroboration of the facts 

 advanced. 



In a letter to Governor Cass, of Michigan, dated September 17, 

 1821, I made the following observations on the subject under 

 review : — 



"I consider the petrified tree discovered during our recent 

 journey up the Illinois, so extraordinary an object in the natural 



