372 THE PLAN OF THE EARTH AND ITS CAUSES. 



low water, subtropical, marine fauna ranged from the Mediterranean 

 to the Caribbean, and can only have crossed along a belt of shallow 

 water in tropical or subtropical latitudes. Direct evidence of the 

 existence of shallow water, continental deposits of the age required is 

 given by the Azores, which, although now separated from Europe by 

 a deep depression, contain shallow water deposits with fossils of the 

 Mediterranean fauna. 



Thus there is strong evidence to show that the Atlantic, in its 

 present form, is of no great geological antiquity, and Suess's theory of 

 its origin continually gains stronger support. Similar, though less 

 complete, evidence shows that the other ocean basins have been broken 

 up along certain lines, and emphatically denies their entire permanence 

 throughout geological times. 



ELIE DE BEAUMONT'S "PENTAGONAL RESEATJ." 



Hence, if the ocean basins were not formed pregeologically, but 

 have grown from the changes that have occurred during the long ages 

 of geological time, then we must seek for a cause that has acted con- 

 tinuously and is acting to-day. A more permanent cause is supplied 

 by the contraction of the earth's crust, as the globe gradually cools. 

 Since the cold, hard crust is less plastic than the hotter interior, it is 

 necessarily crumpled as it is forced into a smaller space. 



This idea is well known, as it has been invoked by geologists to 

 explain the formation of folded mountain chains. That the mountain 

 systems of the world were formed by this agency is improbable; but it 

 is perhaps still too much to say that it is impossible. For Prof. Gr. H. 

 Darwin has suggested that the contractility of the rocky crust has 

 been exaggerated, and it has been shown that Eeade's level of no strain 

 may lie much deeper than was at first thought. 



That secular contraction is the direct cause of the great fold-moun- 

 tain systems is however less widely believed by geologists than it once 

 was; but it may have an important influence in determining their 

 direction. The trend of the great chains of fold mountains is to us a 

 significant question, because there is much truth in the phrase, pro- 

 verbial since its use in 1682 by Burnet in his "Theory of the earth," 

 which describes the mountain chains as the " backbones of the conti- 

 nents." The first geological attempt to explain the plan of the earth 

 was based on this belief. The author of this system was the French 

 geologist Fdie de Beaumont, whose theory of geomorphogeny was stated 

 at length in his " Notice sur les systemes de montagnes" (3 vols., Paris, 

 1852). This famous theory was based on a correlation of the mountain 

 chains by means of their orientation. Erie de Beaumont accepts the 

 view that the earth consists of a thin rigid crust surrounding a fluid, 

 solidifying interior. The crust being thin, it necessarily collapses as 

 the internal mass contracts. He assumes that these collapses occur at 

 intervals of time, and that at these collapses the crust is broken along 



