434 PROCEEDINGS OF THE ACADEMY OF [1897. 



trending channels and to cut them so deeply that they would still 

 remain the water courses after the subsequent depression. The 

 final sinking of the eastern half of the chain, would convert the 

 river channels already cut out of the crystalline rocks into deep 

 lakes lying as it is shown these do, more or less in the same direc- 

 tion and within a belt of moderate width. The currents of the 

 upper courses must have become sluggish and the sources of supply 

 have changed to morasses and swamps. The gentle slope directly to 

 the east would be the natural direction of these streams, instead of 

 as originally before the first elevation of the longitudinal valleys, to 

 the N. and S. Wherever depressions of the level occurred, would 

 be found a lake of greater or less extent and these lakes would 

 increase in number and simplicity of form as the angle of descent 

 became less and the rocks softer. The promontories and deep slopes 

 of the old river-bed lakes which represented the parts of more than 

 usually hard rock where the mountain streams had been deflected, 

 and the deep canons where the maximum erosion had been ac- 

 complished, would be less and less frequently seen, the further one 

 followed the river courses to the east. The production of lakes with 

 and without efflux in the level region would follow as a matter of 

 course as is seen in the courses of the Mississippi, the Volga and 

 other large streams. 



The existence of the third or intermediate type of lake of which 

 M. Karpinsky speaks, lying between those close to the Oural axis 

 and those on the steppes would be very natural in a part of the 

 country where both orographic and petrographic characters were 

 changing from those of the rocks containing the lakes of type I, 

 to those containing the lakes of type II. Finally many of the 

 shallower lakes would be transformed into marshes and swamps. 



On the other hand the existence of large masses of metamor- 

 phosed rocks; of the evidences of distortion and crushing; of rents 

 filled by eruptives and their disintegration products ; the occur- 

 rence of valuable mineral deposits in that part of the mountain 

 system nearest to the axis; would be naturally explained by the 

 dynamic and thermal effects resulting from the regional downthrow. 

 It appears much at least as plausible that such causes acted as that 

 the former eastern counterparts of the rocks constituting the west 

 slope of the Oural have been eroded and redeposited as the rocks of 

 the retreating Tertiary sea. 



