VII. 



DEEP-SEA FORMATIONS. 



The study of oceanic deposits has materially modified many 

 of our notions reo^ardino- the mode of formation of the marine 

 deposits of former geological periods. These deposits consti- 

 tute a considerable portion of the crust of the earth, and we may 

 to-day, as has well been said by Saporta, study their mode of 

 formation, like that of the bads of the chalk, of the oolite, of 

 the miocene, and of the later tertiaries, as plainly as if we had 

 Hved and witnessed the phenomena which have left their record 

 in the geological time tables.^ 



" It is to-day the privilege of the special student to decipher 

 the history of the past with a certain boldness, and from the 

 careful study of the present to picture to himself the most 

 ancient phenomena. Beds composed of globigerinse, of ptero- 

 pods, of fine sand, or of ooze, have long been known to the 

 geologist ; but their interpretation by the knowledge of to-day 

 calls up pictures of the past which his predecessors could never 

 have imao'ined." 



Granting the great age of our oceanic basins, it follows that 

 while there were in earlier geological periods deep-sea deposits 

 similar to those laid down to-day on the floors of our oceans, 

 yet they constitute but a small part of the beds which go to 

 make up the thickness of the earth's crust. Abyssal deposits 

 must always have been formed near the sea-edge of the conti- 

 nental nuclei, or in the track of the principal currents of those 

 days ; while on the continental folds were deposited in succes- 

 sion the formations which have built up our continental areas. 

 Then, as to-day, the coarser materials were deposited within a 

 short distance of the existing shore line, while the coarser sands 



^ Saporta, Gastou de, Revue de Deux Moudes. 



