RELATION OF ISOSTASY TO MOUXTAIX FORMATION 397 



This in turn indicates the significance of the structure of the cores of 

 old mountain masses, where mashing of sediments is evident over the 

 greater j)ortion of the continental nuclei, together with the outer rings 

 of Archeozoic age. Horizontal movements therein must have affected 

 areas many hundreds of miles in width. 



This again points to the inevitable conclusion that mountain-making, 

 from the viewpoint of horizontal manifestations, has been slowing down 

 from the Archeozoic to the present, with a revival in the Cenozoic of 

 localized horizontal movement on a gigantic scale. 



The question, then, naturally arises, "Why should the cores of Archeo- 

 zoic mountains show mashing on the continental scale, while Tertiary 

 ranges show local rings of mashing only ?" This point is considered below. 



Summary and Conclusions 



It would appear from the foregoing summary of observations that the 

 mountains, both of the present and of past periods, have spread out from 

 the continental nuclei in arcuate form toward the Tethyan region on the 

 one hand, and the Pacific, together with the Atlantic, on the other. The 

 Atlantic influence became altogether subordinate to that of the eastern, 

 or Pacific, region proper, with the progress of time. 



Today the Pacific is the main center^^ toward which the continents are 

 creeping. The general result is that the continents are becoming more 

 stable and continuous by the consolidation and the fusion, above sealevel, 

 of mountain rings and intervening land troughs, while the Pacific also 

 inclines toward stability, with a tendency toward contraction of area in 

 its deeper portions. 



The study of the growth of mountain ranges apj^ears to place the 

 hypothesis of the permanence of ocean basins and of the continental areas 

 on a firm footing. 



If the ocean basin be taken as a datum surface, it would appear that 

 the continental masses have flowed or crept in undulations slowly — very 

 slowly indeed — toward the larger ocean deeps. This movement has pro- 

 duced earth crests and troughs — in other words, rhythmic pulsations — 

 the land crests and troughs tending to become mutually supporting 

 through the medium of a lower zone of rock flowage. There is, however, 

 a slight declination of the undulations toward the great ocean basins, and 

 there is a slight tendency to translation of material thither near the 

 surface. 



" The main exception to this is the Tethyan influence. The case of the African moun- 

 tains is not considered in this note. 



