Malott: The "American Bottoms'' Region 21 



THE PRE-GLACIAL PHYSIOGRAPHIC HISTORY OF 

 THE REGION 



The Significance of Land Forms. Having shown that the 

 series of rocks exposed to the various agencies has given 

 rise to a number of primary regional forms dependent upon 

 the characteristics of the strata themselves, and the particu- 

 lar agencies at work, we may turn to the second set of con- 

 ditioning factors mentioned in the Introduction. This second 

 set of conditioning factors has been determined for the most 

 part empirically by a study of the relations of the ''American 

 Bottoms" region to the wider territory of which it forms an 

 integral part, a territory embracing the larger part of the 

 Mississippi valley. The broad diastrophic impulses which 

 have affected the Mississippi valley should be registered in 

 the land forms of any unit area situated in such a central 

 position as southern Indiana. It is maintained that any 

 broad crustal change affecting a great interior continental 

 basin, like the Mississippi valley region, will be recorded in 

 land forms, and that this record will reach in measurable 

 form, the remoter parts of the area affected. The physio- 

 graphic development of southern Indiana when finally read 

 will not be essentially different from the history of the Mis- 

 sissippi valley as a whole, and, turning the statement around, 

 the physiographic development of the Mississippi valley must 

 harmonize with that of southern Indiana. Further, it may 

 be generally stated that any adjustment which has been made 

 by the master stream of a region must be recorded in the 

 streams which are tributary to it. Yet no particular small 

 area has squeezed into it the full physiographic data of the 

 larger territory to which it belongs. Direct data from some 

 one particular area may be applied to another by inference. 

 The particular region here in question by no means has within 

 itself its full readable physiographic development, yet it is 

 being presented here as a representative unit in southern 

 Indiana physiography, which, in turn, must harmonize with 

 that of the Mississippi basin. In so far as any of the con- 

 ditioning factors belong to the second group, viz., those deal- 

 ing with crustal movements separated by periods of crustal 

 stability, have failed to stamp the region with the characters 

 which neighboring regions lead one to expect, by so far it 



