404 SCIENCE PROGRESS. 



chians the first condition seems alone to prevail, the lateral 

 pressure having acted unequally from the oceanic and from 

 the continental sides. 



When a vast thickness of strata has thus been depressed 

 below the surface, the bottom of the geo-synclinal eventu- 

 ally becomes weakened by the heat rising from below, and, 

 partially yielding to the pressure, the rocks become dis- 

 placed, upturned, folded, and fractured. 



In the same year Suess published his volume, Die 

 Entstehung der Alpen, which was destined to at once 

 raise the whole discussion to a higher level than it had 

 ever before attained. The labours of Favre and Lory in 

 Switzerland, Beyrich in Bohemia, Abich in the Caucasus, 

 Stoliczky and Medlicott in India, Von Richthofen in the 

 Carpathians and China, not to mention a number of other 

 observers, were laid under contribution to assist in build- 

 ing up those generalisations, the results of which we enjoy 

 to-day. 



Accepting as his theoretical basis the contraction of the 

 earth's surface, Suess pointed out that the Alps formed 

 part of one enormous belt encircling the globe, and were 

 therefore not merely local occurrences, but component parts 

 of one vast movement. Further, that not merely the 

 central crestal ridges should form the subject of discussion, 

 but that a whole region or series must be taken into ac- 

 count. As a result of his observations, he is of opinion that 

 there are directions of mountain flow, the forward move- 

 ment being marked by the overlapping or overthrust of 

 beds belonging to the Alpine system, over those which have 

 not shared in the movements resulting from contraction ; 

 whilst, in the rear of the mountain-axis, great faults and 

 considerable fractures are produced, these, as in the Apen- 

 nines and Carpathians, occasionally giving rise to important 

 lines of volcanic eruption. 



Not only, therefore, are many of the most magnificent 

 mountain systems asymmetrical, but they have also a de- 

 finite movement, flowing towards, or from, the poles. 

 From the Cordilleras to the Caucasus this flow is uniformly 

 northwards ; whilst across the whole of Asia the conditions, 



