IOWA ACADEMY OF SCIENCES. 



53 



of the two is fully established only in a few cases. One of the 

 most notable instances that we have near us is in the coal 

 measures of the Mississippi basin. A section north and south 

 from the Minnesota line to west-central Arkansas is indicated 

 below (figure 2): 



Figure 2. North ard South Section of Coal Measures of the Western Interior Basin. 



Another, in which the old grade-plain is still unburied is 

 believed to be found in the southern United States in which the 

 Cretaceous, or early Tertiary, peneplain passes under the depos- 

 its of the Mississippi embayment (figure 3) : 



Figure 3. Structure of the Mississippi Embayment. 



It is, however, to some other excellent displays of similar 

 features that attention is especially called at this time, sections 

 on the north shore of the Black sea, that |have been recently 

 noted. 



The Crimea is a peninsula about one-half of the size of Iowa. 

 At the south its surface rises abruptly from the sea to a height 

 of over 4, 000 feet, and then slopes gently down to the northern 

 border, which is nearly at sea level. From almost any com- 

 manding point the general upland plain is distinctly marked, 

 rising gradually to the southward to the top of the mountains 

 of the Tauric chain. The peneplain is of Tertiary age. At 

 a comparatively recent date it has been elevated to its present 

 position. The new cycle of erosion that has begun has brought 

 out into bold relief the hard layers which, with the interven- 

 ing soft beds, had been previously tilted and bevelled. The 

 result has been to produce a remarkable step and platform 

 topography — the Cuesta relief of Hill. At Bakhtchisarai, 

 forty miles northwest of Sevastopol, for example, a profound 

 system of transverse valleys has been opened out, the one side 

 having almost perpendicular cliffs over 500 feet high. The 



