12 A TEXTBOOK OF OCEANOGRAPHY 



endured at least since Mesozoic times,* but the seas of Mediter- 

 ranean type are, geologically speaking, young seas, many of 

 them, in fact, in spite of relatively considérable depths, are of 

 tertiary and some even of post-glacial origin. 



The classification of great water areas according to origin 

 gives us two main types : 



1. The deep sinkings between the main masses of the 

 earth's continents — i.e., the océans. Thèse are of great 

 antiquity geologically speaking, and hâve been permanent 

 since their origin. 



2. The seas formed at the edges of the continents. They 

 are of récent origin geologically, and hâve changed much in 

 récent times. They are of two main types : 



(i) Formed by sinking of the continental crust. 



(2) Formed in breaking of the waters of the océans by 

 dislocation of the earth's crust. 



Seas of the former type are shallow, and the présent sea 

 bottom owes its configuration to previous aerial denudation in 

 the main. Examples : The Baltic, Hudson Bay ; probably the 

 Southern North Sea is also of this type. 



The second type resulting from dislocation of the earth's 

 crust. Example : The Red Sea. 



Gulfs and Bay s. — Thèse are difficult to classify from an 

 océanographie standpoint, since the nomenclature is very 

 confused. Bays, bights, and gulfs hâve slightly différent form 

 as a rule, though the three names hâve been applied at différent 

 times to the same — e.g., Bay of Biscay. It is now impossible 

 to rectify this nomenclature. 



Bays and gulfs are, broadly speaking, of two main types : 



(a) Océan ic. 



(h) Mediterranean — i.e., communicating with the océan 

 indirectly through an enclosed or partially enclosed sea. 



The diversity in form, size, and so on, is so great that any 



* Though their connections hâve altered — e.g., the W}'ville-Thomson 

 ridge may, since Mesozoic times, hâve formed a dry-land connection 

 between America and Europe. 



