March. 1893. ARE OCEAN DEPTHS PERMANENT ? 181 



coasts are not outlined by folded structure, except in the arch of the 

 Lesser Antilles, and in the corresponding short arch passing through 

 Gibraltar, which serves to connect the mountains of north-western 

 Africa with those of the south of Spain. These are what we may call 

 the Pacific and the Atlantic types of oceanic regions. 



Indian geologists have shown how the immense Asiatic mountain 

 waves, moving southwards against the Peninsula, have been dammed 

 back by the resistent Peninsular mass, the Korana Hills, and the 

 wedge-shaped mass of Assam ; so that they actually form distinct 

 arches, separated by deep angles receding to the neighbourhood of 

 Tank, north of Dera Ismail Khan, to the Upper Jhelum and Brahma- 

 putra Valley. In this case we call the Peninsula the " Vorland." 



Now cast a look on the map of the North Pacific, and compare 

 the receding angles which mark the western and the eastern ends of the 

 Aleutian arch, where it abuts against Kamschatka and North-West 

 America. You will remark that this part of the Pacific is a " vorland," 

 and homologous to the Indian Peninsula, whilst the Yellow Sea, 

 Behring Sea, and others lie within the folded region. You may also 

 examine the Mediterranean, and observe that the western half lies 

 wholly within a curved and folded mountain chain (Apennines, Sicily, 

 North Atlas, Gibraltar, Andalusian Cordillera), and that in the 

 eastern half all the part south of Crete and Cyprus and east of Sicily 

 lies on the African " vorland," and the rest on the sunken parts of the 

 Tauro-Dinaric arch. 



In the Atlantic region the mountain folds, as a rule, break off 

 against the ocean {e.g., Brittany coast, Devon and Cornwall, south- 

 west Ireland), or else have their folds facing away from the 

 ocean, as in the case of the Alleghanies, and all other folded zones on 

 the eastern side of North America as far as Newfoundland. The folds 

 disappearing in south-west Ireland and in Brittany so very much 

 resemble those rising from beneath the Atlantic on the coasts of Nova 

 Scotia and New Brunswick, that M. Marcel Bertrand has ventured 

 to publish a sketch-map, showing these chains trending right across 

 the Atlantic. 



There exists a curious tendency for a depression or a sort of 

 valley to form in front of the great folds facing the " vorland." For 

 instance, the depressions of the African desert in front of eastern 

 Atlas, the river valleys in front of the high Indian chains, and the 

 Persian Gulf in front of the Zagros chains. Quite recently the 

 Austrian exploring ship " Pola" found a depth of 4,400 metres near 

 the south-west coast of Greece, near the front of the Dinaric arch ; 

 and some of the greatest oceanic depths show exactly the same 

 position in front of the arches of Japan, the Kuriles, and the Aleutians 

 with Alaska. This is the homology, for example, between the Ganges 

 valley and the Tuscarora depth, both marking the limit of the folded 

 ranges and the " vorland." 



The structure of the earth's crust does not, therefore, tell us that 



