436 STUDIES FOR STUDENTS 



characters have been retained even after cementation and partial 

 metamorphism. 



DEEP-WATER MARINE DEPOSITS 



Deposits of the deep sea, that is, those materials laid in the 

 sea beyond the edge of the continental shelf, are not here described, 

 partly because their position of deposition makes their study in 

 place almost impossible and partly because they are not commonly 

 represented on the lands either in cemented or unconsolidated 

 rocks. They are known, however, to consist of the finest terrige- 

 nous material, remains of pelagic life, submarine volcanic materials, 

 atmospheric dust, extra-terrestrial materials, and the results of 

 chemical alteration of the above-mentioned substances. Pre- 

 sumably most of it is finely divided, has a low textural range, 

 and lies in horizontal strata. The fossils are doubtless pelagic in 

 character. 



An attempt is made to condense all the important characters 

 in the foregoing lists into a single table which may be used as a 

 key to the identification of the various common sediments. 



