152 MISSOURI BOTANICAL GARDEN. 



gone to make iip^ the soil in its present condition. This or- 

 ganic matter has furnished the carbonaceous material to 

 which the black color^ of the soil is mainly due, and the phos- 

 phates, the ammonia and other animal substances which have 

 added greatly to its productive qualities. 



*^The presence of these deposits over nearly the entire sur- 

 face of the State, gives that uniform character to the soil 

 which forms so marked a feature in its surface geology and 

 makes it one of the finest agricultural regions on the face of 



(-jx^^v^x^v^.^x x^^ 



the globe- The soils based upon the loess contain a smaller 

 amount of alumina and a larger percent of silica than the 

 ordinary drift soils, and from the porous nature of the subsoil 

 it absorbs water freely, and withstands the extremes of both 

 wet and dry seasons much better than the ordinary clay 

 soils. The calcareous and marly portions of the loess may be 

 used to advantage as a fertilizer on sour and wet clay soils." 



Physiography, 



The entire section under consideration formed at one time 

 part of an extensive peneplain, the result of a former cycle of 

 erosion at a time when the land stood lower than it does now. 

 As pointed out by Marbut,* it could be reconstructed at the 

 present day by filling up the valleys. This author further 

 points out that by comparison of the stage of development 

 of this peneplain with that reached by another, the geological 

 age of which can be decided by tracing it to its shoreline 

 and determining the age of the rocks which lie upon it or 

 which were deposited just before the uprising, the geological 

 age of the Missouri peneplani can be arrived at. A compari- 

 son with the Appalachian region places the completion of 

 the Missouri peneplain not earlier than middle or late Ter- 

 tiary time. During the glacial period and subsequent to it 

 this plateau underwent first the changes due to the presence 

 of a large and rapidly moving body of water streaming 

 southeastward and carrying with it a large amount of detritus. 

 As the result a valley was scooped out which later was par- 



* Marbut, C. F. Physical Features of Missouri. Missouri Geological 

 Survey. 10 : 24. 1896. 



