80 F. p. GULLIVER PLANATION AND DISSECTION OF URAL MOUNTAINS 



the Sim and Ufa rivers, in the region where the Permian rocks are chang- 

 ing from the horizontal to the folded structure in that transition field 

 between plains and mountains. The section in this region (figure 4) is 

 therefore of great importance in connecting the grade-plains in the moun- 

 tains with the uplands of the plains. The party was not in this region 



S.E. 



KW. 



FiGUKE i. — Section at Ufa. 



long enough to allow any excursions back on the uplands, but from what 

 the writer saw he is inclined to group the upland level («, of figure 4) of 

 this region with the first grade-plain formed beneatli the upland in other 

 sections (see s -|- 1, ^ + 1, etcetera, of figures 5 and 6). In these sections 

 the writer has given a different letter to each ; in all cases representing 

 the upland by the simple letter and giving the successive grade-plains 

 formed beneath the upland the same letter, with + l,-f2, etcetera, added. 

 There are two aggradation plains above the present river channels in 

 this region, the upper terrace representing the late Caspian expansion 

 and the lower an alluvial terrace, formed since the Caspian stage. 



GEADE-PLAINS NEAR SIMSK 



Along the Sim river the writer went up several times on the grade- 

 plains above the river, and it appears quite possible that the upland at 

 Simsk (s, of figure 5) and the grade-))lain next beneath it (s + 1) grad- 

 ually approach each other and meet somewhere near Ufa. This would 

 mean that the first up-arching of the Urals, after the long period of plana- 

 tion, did not extend farther west than the area between Simsk and Ufa. 

 The uplands in this whole region should becarefull}' studied to test this 



Figure 5. — Simsk Grade-plains. 



At Simsk were two well marked dissection grades between the upland 

 and the present river grade (figure 5). The estimated relations in ele- 

 vation of these plains is as follows : s -j- 2 is 80 to 100 meters above the 



