Malott: The " Ayiierican Bottoms'' Region 



59 



the physiographic agencies have imprinted their forms. The 

 material on which the processes react is of prime importance 

 in giving rise to topographic forms. A knowledge of the 

 geology of a region goes far in explaining the type of topog- 

 raphy present. The second set of conditioning factors con- 

 sists of the broad crustal movements which have decidedly 

 changed the stream regimen, and consequently have caused 

 certain physiographic forms of more or less wide distribu- 

 tion. The third conditioning factor is glaciation, of such a 

 sort that a triangular area in the middle western portion of 

 southern Indiana has been left unglaciated. The fourth factor 

 is the drainage to the west and south. This factor is related 

 to all the others, but bears a specific and peculiar relation to 

 the glaciation. The latter combination has given rise to very 

 peculiar physiographic relationships and topographic forms. 

 The particulars of these conditioning factors need not be re- 

 peated in this summary. 



The "American Bottoms" region of eastern Greene County 

 is used as a type unit in southern Indiana physiography. This 

 region is mainly located within the unglaciated area, but laps 

 over into the glaciated portion to the west. Its drainage 

 arises in the unglaciated part and flows toward and into the 

 region formerly covered by the ice. The topography of the 

 region is representative of the rougher and more dissected 

 part of the state, having an immediate relief of some 250 

 feet. The drainage is peculiar, in that a broad, flat basin 

 known as the "American Bottoms" has a subterranean drain- 

 age of a very unusual character. 



The rocks of the "American Bottoms" region consist chiefly 

 of several stratigraphic units of the Chester Series of the 

 upper Mississippian. The ridges of the region are capped by 

 the Mansfield sandstone of the Lower Pennsylvanian. The 

 stratigraphic series contain several lithologic types which give 

 rise to certain regional forms inherent in the particular litho- 

 logic type. The Beech Creek limestone, the Cypress sand- 

 stone, and the Mansfield sandstone are of high importance 

 in controlling topographic forms. The Beech Creek limestone 

 is especially important, not only for the topographic forms 

 it gives rise to, but because it becomes a controlling physio- 

 graphic factor. The peculiar underground drainage of the 

 "American Bottoms" basin is thru the limestone. 



