28 .lOUKXAL OF THE 



McGee's objection is done away with by the fact that 

 the Susquehanna River is not situated in a region of the 

 required horizontal homogeniety, and tliat if it now shows 

 a preference for its left bank, that preference is probably 

 an inheritance from the time when the favoring conditions 

 did exist, before its superimposition upon the Wiconisco 

 and Tuscarora-IMahanoy synclines, when the course of the 

 river was the reverse of what it is now, and its present left 

 bank was its right bank.* 



Turning now to the regions of horizontal homogeniety, 

 we see that their streams all show this right or left deflec- 

 tion, according as they are north or south of the equator. 

 Such a region is that where the phenomenon was first 

 observed, in the middle and lower courses of the Volga. 

 Here all of the conditions are most favorable; the river has 

 a considerable length of course, and the mass of water is 

 powerful enough to clear away any obstacles; ''there are 

 enormous floods which periodically increase the force of 

 erosion in the currents, and the cliffs are composed of fria- 

 ble rocks, "t Two centuries ago the principal mouth of 

 the Volga flowed directly to the east of Astrakhan; since 

 that time the great current has successively hollowed out 

 for itself fresh beds, tending more and more to the right, 

 and at the present day the branch navigated by vessels 

 turns to the south-south-west. The Volga, up to its near 

 approach to the sea, has a high right bank, and the erosion- 

 valley, which slopes gently on the left, is bounded by 

 rather abrupt cliffs on the right. 



Fic. I.— The Volga and the Rwjaga. 



*See Rivers and Valleys of Pennsylvania, W. M. Davis, National Geographic Maga- 

 zine, Vol. I, p. 47, 1S89. 

 fVon Baer. 



