1897.] NATURAL SCIENCES OF PHILADELPHIA. 411 



caps the beds of Zechstein fauna, and the other lies below the Zech- 

 stein, corresponding in part with its lowest horizons. 



As approach is made to Oufa one after the other of the dis- 

 tinguishing beds in the two formations rises slowly and loses itself 

 farther east on the tops of the nearest hills. The gray group of 

 schistose limestone and marls intercalated with friable sandstone 

 marking next to the uppermost member of the Permian, recognized 

 by the Russian Survey, shows itself for the last time on the summit 

 of Yarych-Taou, the last of the conical mountains of erosion along 

 the Dioma. The appearance of a red group in the sections near 

 Oufa has caused many geologists to ascribe this horizon to the 

 Tartarian, which the geologists of the survey hold to be an error, 

 maintaining that the ravines and sections establish beyond doubt 

 that the measures increase in age as one goes eastward. 



Oufa may be properly said to lie on the line which marks the 

 foot of the Ourals, because at about this distance from the axis of the 

 Oural chain the streams having broken through the west flanking 

 foot hills of the main chain take the final courses to fulfil their 

 ultimate destiny of irrigating and fructifying the trans- Volgian 

 steppes. 



The Permian plateau on which Oufa stands is cut by three 

 rivers : the Oufa, the Sim, and the Bieleia, into three elevated 

 plateaux separated by deep and rich valleys. The immediate neigh- 

 borhood of Oufa has not furnished distinctive fossils, but the sections 

 along the Bieleia and its affluents have convinced the geological 

 surveyors that the upper part of the section at Oufa corresponds 

 with the lower Permian red bed which is capped by the gray arena- 

 ceous Zechstein bed, richly furnished with fossils that can be seen in 

 the sections of Slak, the mountains Yarych-Taou, etc., between 

 Samara and Oufa. The lower gypsiferous and calco-gypsiferous bed 

 at the base of the Oufa section can be seen to have intimate relations 

 with the gray, compact, tile-like limestones, and dolomites, and the 

 cavernous, spotted brecciform limestones containing many casts of 

 Beilerophon, remains of Productus and Orthoceras, accompanied by 

 Schizodus truncatus, Astarte Pernio- Car bonico, Macrodium kingia- 

 num, and corresponds to the lower Zechstein of southern and central 

 Russia, situated below the lowest bed of Permian red. [See L. G., 

 III.] 



As an aid in understanding the orography of the western half of 

 the Ourals (from which the eastern half is entirely different) let it be 



