ECOLOGICAL CROSS SECTION OF THE MISSISSIPPI. 159 



-I 



elevation, 



fcrrcd 



d 



the dead. But the simple fact that they were used for this 

 purpose by the aborigines, which seems to be the main argu- 

 ment relied on as a proof of their artificial origin, seems to me 



and 



by them 



same 



selected the highest point of a bluff, in preference to any lower 

 point; to serve as the last resting place for the earthly bodies 

 of their relatives and friends. I have very little doubt that 

 many of the so-called Indian Mounds, in this State at least, if 

 carefully examined, would prove to be only natural elevations 

 nrndncf^d bv the causes above named. ^' 



American Bottom is bordered 



Lcal formation. 



Missouri 



and 



fan-shaped slopes. The ordinarily flat, sometimes undulat- 

 ing tracts, which compose the Illinois plateau, situated 

 from 500 to 600 feet above sea-level, are divided by narrow 

 strips of woodland bordering the creeks and rivers and are 

 covered by a rich soil. The water table of the country is but 

 little inclined and the streams have but a moderate descent. 

 Owing to this, the decaying vegetable matter is not carried 

 off and the rainwater becomes stagnant, resulting in un- 

 healthful conditions. Sinkholes are frequent. Near the bluffs 

 often occur strips of woodland. 



• THE FLORA. 



Plant Societies, 



The plant societies which are here analyzed successively 

 from the table-land on the Missouri side of the Mississippi 

 River, to the table-land on the Illinois side, agree very closely 

 with those indicated by Daniels,* the component species, for 

 the greater part at least, being also identical with those in 

 the region studied, the differences which exist being evident 

 from the following; detailed analysis. 



Daniels, F. P. The Flora of Columbia^ Missouri and Vicinity. The 

 University of Missouri Studies. Science Series. V. 1907. 



