408 PROCEEDINGS OF THE ACADEMY OF [1897. 



Productus giganteus and finally to the lower coal in the neighbor- 

 hood of Riajsk and Skopine. The quaternary boulder clay of 

 this region contains large blocks of crystalline and quartzitic rocks 

 from Finland. All these quaternary deposits of this region are 

 covered by a dark brown or black soil, which the Russian investi- 

 gators agree to divide into two classes. 1st. the " tschernozem " 

 properly so-called, which is dark brown or black, 0'5 meter or 

 more in thickness, rich in humus, lime and zeolites, formed in 

 place by the alteration of various superficial deposits, etc. 



2. Forest earth, also dark brown or black, but of different physico- 

 chemical constitution. 



It may be true, however, that the tschernozem of the steppes 

 when covered by forests is gradually transformed into forest earth. 

 These two kinds of soil and the resulting steppe and forest alter- 

 nate in the region between the Pronia and the Volga. The line 

 of route from Riajsk through Pensa to the neighborhood of Syzran 

 follows the great trans-Siberian railway over upper Cretacic and 

 lower Tertiary steppes of moderate glacial interest, and considerable 

 monotony, but at the latter place there is an abrupt change. 



About 760 km. from Moscow by railway, or 1,400 km. from the 

 head-waters of the Volga not far from St. Petersburg, a sudden 

 change in the landscape and surroundings on close approach to the 

 great river indicates that some special forces have been at work in 

 this neighborhood. In the first place, the Volga, after pursuing a 

 generally south direction from Kazan, abruptly turns to the east 

 for about sixty kilometers while skirting the north flank of the 

 Jegouli Mountains, but here breaking through them perpendicular to 

 the axis of their prolongation, and leaving a large enough mass on 

 the left bank to act as one of the two posts of the gates of Samara, it 

 returns in a direction parallel and opposite to that by which it had 

 come, and finally resumes its southerly course with some slight westing 

 toward the Caspian Sea, distant about 1,000 kilometers. It appears 

 that a gentle anticlinal, with an axis running northerly, and recog- 

 nized further to the north in the tilted Permian limestones of the 

 right bank of the Volga, has suffered a local dislocation resulting 

 in a fault cutting through it almost at right angles, and bent in the 

 west flank. The fault passes along the north side of the peninsula, 

 which is called Samarskaia Louka, after the large city opposite its 

 extreme point. Both sides of this fault-line the measures dip 

 S.S.E., but the north side has been depressed, while that to the south 



