3 UNIVERSITY OF MISSOURI STUDIES 



River, but elsewhere along its course in this area the valley bot- 

 tom is but slightly wider than the river channel. The stage of 

 development of the valleys is typical of mature topography. 

 Thruout the area the valleys are steep-sided, and the streams 

 reach grade within short distances of their sources. The head of 

 a valley has a slope almost as steep as that of the sides. If the 

 surface could be inverted the resulting ridges which are now 

 valleys would be remarkably like the present ridges. 



Most of the streams are working on rock floors, the excep- 

 tions being those in the northern part of the area, north of Min- 

 eral Fork, where the ridges are being cleared of timber for agri- 

 cultural purposes. Clearing has caused a large amount of mate- 

 rial to be swept down into the channels of the streams, so much 

 so in many instances that agricultural lands on the bottoms are 

 being buried, and the stream channels are in gravel. In some in- 

 stances the gradient in the upper parts of the streams is suffi- 

 cient to enable the streams to sweep all the debris down to the 

 lower courses. 



There is no evidence of structural control along any of the 

 streams. The rocks, as a rule, do not depart much from a hori- 

 zontal position, so the effects of rock structure would be con- 

 fined to the formation of ledges or terraces dependent upon the 

 relative resistance of the formation. The topographic effects of 

 structure are slight. 



Physiographic record. — The remarkable accordance in ele- 

 vation of the summits of the ridges leads to the conclusion that 

 this surface was a peneplain or base-leveled surface. This sur- 

 face slopes to the north at the rate of about nine feet per mile. 

 Whether this slope is that of the peneplain after it was uplifted, 

 or whether movements have changed the slope since the surface 

 was uplifted has not been determined. 



It is generally held by those who have studied the Ozark 

 Plateau that the area was peneplained during Mesozoic and Ter- 

 tiary times. As to whether this peneplanation began during 

 Mesozoic times there is little but analogy to guide one in decid- 

 ing. No Cretaceous deposits have been found in Missouri, altho 

 there are formations of Cretaceous age in Iowa and Nebraska 

 only 40 to 50 miles from the Missouri border. From the south- 



