82 F. p. GULLIVER rLAXATION AND DISSECTION OF URAL MOUNTAINS 



wliere all three occur together and always with the same relative eleva- 

 tion and ])readth; therefore this ])oint is i)eculiarly favorable for begin- 

 ning a thorough study of the^stages of dissection of the Urals. 



FniiHiE S. — Torjanai Srctioii. 



A pliotograph was taken west of Zlatoust, looking toward Ural Taou 

 (plate ,10, figure 3). This view was taken a few meters above the level 

 of the grade-plain (t + 1, of figure 8), in order to show the successive 

 ridges rising to accordant elevations. 



A second photograph (plate 10, figure 4) was taken from the foot of 

 Urenga mountain a little above the grade-plain (t-\- 2). This shows a 

 lake on t -f 2 (of figure 8), a glimpse of ^ -]- 1, the summit ofthe Ural Taou 

 forming t, and Alexandrovskaia peak which is a typical monadnock. 



DISSECTION WEST OF ILMEN MOVNTAIN 



The divide in the Urals passed, the same grade-plains are seen be- 

 tween Alexandrovskaia and Ilmen mountains ; the same relations hold 

 also at several j^laces farther north on the east slope. The steep fall-off 

 has been mentioned, and a suggestion made to account for it. 



Conclusions 



Although not all the facts of topographic form are explained by his 

 tentative outline of the histor}^ ofthe Urals, still there are so many facts 

 which support it that the writer advances with some confidence the fol- 

 lowing working hypothesis : 



First, a long period of subaerial 2:»lanation, leaving a few monadnocks, 

 aided on the margin by marine planation, the limits of which are not as 

 3^et worked out ; second, an up-arching ofthe Urals, the axis ofthe move- 

 ment and the line of greatest uplift being a little east of the middle of 

 the mountains; third, a long period of stream dissection forming broad 

 plains on the less resistant rocks ; fourth, a second up-arching, generally 

 of less amount than the first, with the axis (in the region studied) not 

 far from the first; fifth, a second period of stream cutting, not so long as 

 the first; sixth, a third up-arching; seventh, the cutting of the present 

 stream grades, during Avhich time occurred the Caspian expansion. 



