6 UNIVERSITY OF MISSOURI STUDIES 



gives a maximum difference in elevation for the area of about 

 700 feet. The average rehef, however, is about 200 feet. 



The region, as a whole, is completely dissected, there being 

 no areas that are not entirely in slope. The ridges do not have 

 flat tops and generally are very narrow, some of them being so 

 narrow that the drainage from the two wheel tracks of a v/agon 

 road flows into widely separated creeks. The crests of these 

 long ridges are marked by numerous small knolls and sags. 



Plateaus and escarpments. — There is a marked escarpment, 

 due to the Gasconade formation, which begins nearly two miles 

 west of Hopewell, and follows a slightly northwest direction to 

 a point southeast of Old Mines, thence swinging northwest and 

 going out of the area due north of Richwoods. West of this 

 escarpment the surface declines from an elevation of about 1,250 

 feet at the south to about 1,050 feet at the north, and the plateau 

 to the east of the escarpment has an elevation of about 1,050 

 feet at the south and about 850 feet at the north. This differ- 

 ence of about 200 feet on opposite sides of the escarpment is just 

 about the thickness of the Gasconade formation as found over 

 the larger part of the area. The dip of the beds is not parallel 

 to the slope of the surface, altho on the whole the beds dip to the 

 north. The escarpment is due to the great resistance of the Gas- 

 conade formation. 



Marbut,^ in his discussion of the physical features of this 

 region, has called this the Potosi Escarpment, the plain to the 

 east the Summit Platform, and the upland to the west the Salem 

 Platform. The latter extends to the western part of the state 

 and includes practically all of the Ozark Plateau. In his map of 

 the physiographic belts and platforms (plate 2 of the above re- 

 port) Marbut has the Summit Platform stopping at about the 

 northern end of Washington County. There would seem to be 

 little reason for so limiting it for the region to the north is cer- 

 tainly a continuation of it. He correctly interprets the Potosi 

 Escarpment as being due to a resistant member of the Ozark 

 Series, but of course, he could not tell which formation it was, 

 since the geology of the region had not been worked out. 



'Marbut, C. F., "The Physical Features of Missouri," Mo. Geol. Surv 

 vol. X, p. 37. 1896. 



