112 The American Geologist. February, looi. 
known telegraph plateau on which the cables rest may mark the 
site of this sunken land. Palseontological evidence also sup- 
ports the formation of the Atlantic by subsidence ; for a shal- 
low water, sub-tropical, marine fauna ranged from the Med- 
iterranean to the Caribbean, and can only have crossed along a 
belt of shallow water in tropical or sub-tropical latitudes. Di- 
rect evidence of the existence of shallow water, continental de- 
posits of the age required is given by the Azores, which, al- 
though now separated from Eurooe by a deep depression, con- 
tain 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' 
theor}' of its origin continually gains stronger support. Sim- 
ilar, though less complete, evidence shows that the other ocean 
basins have been broken up along certain lines, and emphatic- 
ally denies their entire permanence throughout geological 
times. 
ELiE DE Beaumont's ""pentagonal reseau." 
Hence, if the ocean basins were not formed pre-geological- 
ly, 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 continuously, and is acting today. A more per- 
manent 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 w'ell known, as it has been invoked by ge- 
ologists 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. G. H. Darwin has suggested 
that the contractility of the rocky crust has been exaggerated, 
and it has been shown that Reade'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-mountain systems is however less widely believed by geol- 
ogists than it once was ; but it may have an important influence 
in determining their direction. The trend of the great chains 
