432 PROCEEDINGS OF THE ACADEMY OF [1897. 



" The presence of lakes nearly always point to recent disturbances 

 in the drainage." 



Recognized causes of lakes are : — 



1. Glacial action. 



2. Volcanic action — crater hollows and lava dams. 



3. Chemical solution — producing inequalities. 



4. Epeirogenic movements — phenomena associated with draining 

 of newly established marine plains. 



5. Sluggish stream action in deltas and flood plains. 



6. Minor warpings of the earth's crust — causing changes of 

 gradient in streams. 



Of course we readily rule out causes 1 and 2 here. There is 

 no evidence of recent glacial or volcanic action in this region under 

 discussion. 



Cause No. 3 would find some advocates as applicable here; but 

 evidence in favor of lakes being formed in this way is meagre. 



Cause No. 4 could have hardly operated here, though it may 

 have had influence in the case of the salt lakes of the Siberian steppe 

 region farther to the eastward. 



" No. 5 must also be ruled out ; we are not dealing with lower 

 stream course phenomena." 



" We seem limited to Cause No. 6. Fig. B represents supposed 

 section of district "A" just prior to the development of the lakes and 

 the gorge. We have here in the dotted line the low stream gradient 

 of a plain lying at base level. Suppose a gentle warping of the 

 earth's crust to produce a fold (not a fault) with an axis parallel 

 with the main chain of the Ourals. This is represented on an exag- 

 gerated scale in Fig. " C." Such a fold thrown across the paths of 

 these eastward flowing streams would increase the gradient of that 

 portion of their courses on the eastward half or limb of this low 

 anticline. The erosive power of the streams would be intensified in 

 this portion of their course. They would tend to cut gorges. In 

 the upper course of the streams, that portion between the developing 

 anticline and the Oural-Taou, the gradient would be lowered, perhaps 

 e ven reversed, for the movement upward on the western limb of the 

 anticline would act in opposition to the current, and form a barrier, 

 which would tend to dam up the waters behind it. In addition to 

 this there would probably be a downward synclinal movement in the 

 region between the anticline and the Oural-Taou. The floor of the 

 syncline would not only be relatively but absolutely lower than it 



