W. H. Twehetrees-The S.W. Slopes of the Urals. 407 



on which to calculate the total cubic contents of the sea, and of the 

 supposed glaciers, it is difficult to form any good estimate of the 

 change of level that would result from such a cause. If there was 

 an ice-cap at both poles at the same time, the centre of the gravity 

 of the earth would remain much as it is, and the cause of sub- 

 mergence invoked by Dr. CroU and M. Adhemar would not come 

 into operation. 



[To be concluded in our next Number.) 



IV. — Notes on the Geology of the Country at the Base of the 

 S.W. Slopes of the Urals. 



By W. H. TWELTETREES, F.G.S. 



THE country at the base of and forming the south-western slope 

 of the Urals has been little visited by geologists from Western 

 Europe, and deserves more attention than it has received. Several 

 years' residence in it form my excuse for recording a few notes 

 thereon. The area I have travelled over extends from Samara on 

 the Volga in the W. to Preobrajensky and Bieloretzky in the E., 

 and from Orenburg in the S. to the town of Ufa in the N. The 

 formations met with within these limits are the Silurian, Devonian, 

 Carboniferous, Permian, and Jurassic. The three former are the 

 crystalline rocks of the Urals, the western edge or front range being 

 composed of Carboniferous grits and limestones. The foot hills are 

 Lower Permian, made up of gypsum, red sandstones and marls, 

 conglomerates, and different varieties of rather homogeneous, com- 

 pact limestone. This division of the Permian, which only in places 

 yields Unios or Anodons and plant-remains, gives way further west 

 to the highly fossiliferous Magnesian Limestone, upon which repose 

 the copper-bearing marls and sandstone of the great Permian steppe. 

 A journey due E. from Kargalinsk over the Lower Permian 

 country to the Carboniferous mountain rocks showed the conglo- 

 merates and sandstones undulating in gentle flexures to within five 

 miles of the front range, and then they dip to the W. The lowest 

 of the Permians was a band of massive gypsum. Five miles further 

 N. the same band was met with, and eighty miles still further to the 

 N.W. the gypsum preserved the same relative position. The out- 

 lying conical Carboniferous Limestone hills at Sterlitamak in the 

 Ufa government, which have burst through the Lower Permian rocks, 

 bring the same gypsum up, which is to be seen at their eastern and 

 southern bases. The band of gypsum first referred to lay on the 

 W. side of the Ik, and the alluvium of the valley obscured any 

 succeeding rocks. Those on the other side of the river were the 

 grits and sandstones of the Carboniferous dipping E. towards the 

 mountains. These were succeeded by the grey crystalline Carbon- 

 iferous Limestone also dipping uniformly in the same direction. 

 Here then the Permian and Carboniferous would appear to be un- 

 conformable. Further N.W., near Voskresensk, the Carboniferous 

 Limestone dips W., and is succeeded by overlying sandstones and 

 coaly flags with plant-remains thinly developed, and these, which 

 are apparently here the uppermost members of that formation, are 



