1897.] NATURAL SCIENCES OF PHILADELPHIA. 421 



Oufa may be resumed in the letters employed by the Russian Survey, 

 as Permian (P), Permo-Carbonic (PC), Carbonic (C), Devonic (D), 

 and finally the material which constitutes the divide called M, and 

 thought by the official geologists to be metamorphosed Devonic. 



It is supposed that the upper and lower black schists are part of 

 D} g and that D} c and Df are conformable with them. The 

 demonstration turns upon this. Beneath D\ c come the schists 

 and quartzites marked metamorphic. It does not clearly appear 

 how the limestones are superposed on it, but unless M be altered 

 Devonic, this is of minor importance. No one would dream of 

 calling in question the accuracy of the Russian geologists who have 

 proposed this structure, without weeks or months of hard and 

 patient labor in the field. To do so would be to show an unpardon- 

 able ignorance of the difficulties of the problem and a poor recogni- 

 tion of the accurate work which these gentlemen have accomplished. 

 But they will not consider it disrespectful if some of their recent 

 guests declare that they are not entirely convinced of the Devonic 

 character of these quartzites and schists which form the Oural divide. 

 Only general considerations extenuating this inability to accept the 

 Russian Survey's determination as final are here in order. In the 

 first place the time was not sufficient to observe the contacts M-D} c 

 and Dl c-D} g, and DJ g-Df . The first two of these are nowhere so 

 explicitly stated in the Livret Guide as to establish the impossibility 

 of faults. The absence of fossils where these beds were seen deprives 

 us of much needed light. Then again the absence of such impor- 

 tant orographic elements as the entire Siluric, Cambric, and 

 Archean is very hard to accept, especially after the investigations 

 of Murchison. The question is one of the highest interest and 

 importance, and it is hoped that more light may be shed upon it in 

 the near future. 



There is another consideration which it must be confessed aids in 

 preventing an immediate and unquestioning acceptance of the 

 Russian structure, although it cannot be dignified by the title of 

 an argument, and can be mentioned as an analogy only and with 

 every reserve. Taken, however, together with the other considera- 

 tions, it is not entirely destitute of weight : — 



If we might for the moment leave out of consideration the horizon 

 of the limestone D} c, and its determination as Devonic we find 

 petrographically an analogy too strong to be overlooked between 

 the sequence of the formations from the crystalline eruptives and 



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