38 TRANSACTIONS OF THE ILLINOIS 



of the prairies around the lakes, and of those of the broad, flat bottoms 

 of our southern rivers ; of the plates of the Madeira river ; of those of 

 the Paraguay ; of the pampas of Brazil ; even of the desert plains of our 

 western Salt Lakes — for this formation is produced in the same manner 

 in the salt marshes of the sea, as in the fresh-Avater swamps of our lakes." 



Hence, Mr. Lesquereux ascribes the original absence of tree-growth 

 to the nature and condition of the soil. " This peculiarity of formation 

 explains, first, the peculiar nature of the soil of the prairies. It is neither 

 peat nor humus, but a black, soft mould impregnated with a large pro- 

 portion of ulmic acid, produced by the slow decomposition, mostly under 

 water, of aquatic plants, and thus partaking as much of the nature of the 

 peat as of that of the true humus." In all the depressions of the prairies, 

 where water is permanent and unmixed with particles of mineral matter, 

 the ground is true peat. 



"It is easy to understand why trees cannot grow on such a kind of 

 ground. The germination of seeds of arborescent plants needs the free 

 access of oxygen for its development ; and the trees, especially in their 

 youth, absorb by the roots a great amount of air, and demand a solid 

 point of attachment to fix themselves." 



He adds that the Tamarac is the only species of tree that will grow 

 in a peaty ground in the northern climate ; and suggests for planting on 

 prairie soils, trees that will support a certain degree of humidity — such as 

 Elms, Sycamore and Honey Locust. 



Henry Englemann, also at one time engaged on our Geological Sur- 

 vey, in an examination of the cause producing the prairies, flats and bar- 

 rens of Southern Illinois, says of the southern prairies : " Undoubtedly 

 the condition of humidity of the soil exercises here the most prominent 

 influence on its vegetation. The chemical composition of the soil natu- 

 rally also affects the flora; but as our prairie soils do not appear to have 

 any very peculiar composition, chemistry may account for the absence of 

 certain species of trees, but certainly not for the absence of all trees." 



The soil of the southern part of the State, I may add, seems to have 

 little of the peaty character of the soil of Northern and Central Illinois. 

 It is more finely subdivided, having a silt-like appearance, as though de- 

 posited in the still water at the lower end of a lake that deposited the 

 coarser material farther north. 



But in both cases there was an original unfitness for tree growth, 

 covering a much larger part of our State than at present, caused simply 

 by humidity. Within the last thirty years, as many here present can 

 testify, there has been a great change. I can remember, and so can many 

 others, when fields now dry enough for cultivation were covered with 

 water for weeks in the winter and spring, and were regarded as of no prac- 

 tical value. But as flocks and herds have eaten off the grass and let in 

 the sunlight, the work of gradual drainage and amelioration already going 

 on has been greatly accelerated. 



It was also found to be the case, in my own region at least, that 

 lands that had already prior to settlement under natural influences, ap- 

 parently, become fitted for tree growth were kept in the condition of 



