Malott: The "American Bottoms^' Region 35 



had developed in it small caves in the greatly enlarged joints 

 Springs flowed from these small caves thru steep gorges with 

 rock-walled heads, similar to the one at Ray's Cave today. 

 Thus, it will be seen that the ''American Bottoms" region 

 has a mature topography with a relief very much like that 

 of the Beech Creek portion of the ''Bottoms" and the vicinity 

 of the upper part of Cliffy Creek. The youthful condition 

 now characterizing the "American Bottoms" had not yet come 

 into existence, and the drainage of that portion was very 

 different from the present. 



Summary of Pre-glacial Physiographic Development. The 



pre-glacial physiography of southern Indiana may be sum- 

 marized as follows : 



1. A long-continued period of erosion gave rise to a wide- 

 spread peneplain. This peneplanation was probably completed 

 in middle Tertiary times. The peneplain developed in southern 

 Indiana is called the Kirksvillc plain. The broad undulating 

 ridges rising near the 800-foot contour represent the Kirks- 

 ville peneplain in the "American Bottoms" region. 



2. An uplift followed amounting to 150 feet or more in 

 the Indiana region adjacent to the "American Bottoms" and 

 widely affected the Mississippi valley. 



3. The Kirksville peneplain was trenched by streams, and 

 gradation planes and local peneplains developed in regions 

 of unresistant strata. This stream trenching is well developed 

 in the "American Bottoms" region; but gradation planes or 

 local peneplains do not seem to have been produced. 



4. The erosion cycle when well begun was interrupted by 

 further uplift, amounting to some 250 feet or more in south- 

 ern Indiana adjacent to the "American Bottoms" region. 



5. The streams were then incised in response to the re- 

 juvenation of the land, and the main streams were cut from 

 0 to 150 feet below the level of the present valleys. The 

 mouth of Plummers Creek, some 3 miles west of the "Ameri- 

 can Bottoms" region, must have been cut at least 100 feet 

 below the present valley level. 



6. A period of valley filling ensued, and the valleys were 

 filled from 0 to 150 feet or more in the middle Mississippi 

 valley region. This valley filling has ordinarily been inter- 

 preted as the result of regional depression, but an alternative 

 view is suggested here to the eifect that the valley filling has 



