430 PROCEEDINGS OF THE ACADEMY OF [1897. 



met with) and the cutting of all the sedimentary rocks by the 

 massives. The rocks above mentioned occur sometimes in their 

 natural order, but often without any regularity whatever. The 

 beds generally do not dip with the slope but to the west. In 

 proportion to the distance from the axis of the chain the stratifica- 

 tion becomes less deranged and the metamorphism feebler, never- 

 theless on the eastern slope up to the appearance of the tertiary 

 deposits in force the different formations alternate without any order. 

 The conclusion of M. Karpinsky is that the principal abrasion of 

 the region has been due to the invasion of the tertiary sea (paleogene), 

 and a considerable part of these deposits have been formed at the 

 expense of the older rocks then rising above the present level of 

 the country. The difference in the geological structure in the two 

 sides of the Oural is reflected in their mineral wealth. Thus the 

 stratified deposits, such as limonite, cupriferous sand and coal, are 

 found principally on the west side of the chain, while the vein or 

 massive deposits are found on the east : the placers are the only 

 stratified deposits of minerals peculiar to the east side. 



After the above, which is the resume by M. Karpinsky of the 

 structure of the east slope of the Oural, 5 it is, perhaps, the best place 

 to consider the interesting question of the cause of this structure 

 which the travellers over the route of the excursion have verified as 

 accurately stated. Several points have been emphasized above to 

 call attention to the part which they bear to the hypothesis advanced 

 by one of these excursionists. 



Prof. Gotz of Munich is of the opinion that but two hypotheses are 

 tenable. The first is naturally that the lake basins have been 

 ploughed out by ice or other powerful physical agents (which he 

 concludes cannot be maintained), and the others that they are due 

 to atmospheric agencies — chemical and mechanical. 



The writer's first suggestion, which he afterwards found had been 

 advanced independently by Prof. I. C. White, was that the sub- 

 jacent limestones had been dissolved out by waters percolating the 

 soil and the depressions thus formed had been filled with water. 



The following is the hypothesis of Prof. Arthur M. Miller, of 

 the State College of Kentucky, Lexington, Ky. : 



"A" (Figure 2) represents the course of a tributary stream of the 

 Irtysch, draining the Asiatic slope of the Ourals. 



6 L. G., V. 



