144 



DEPTHS OF THE OCEAN 



Number of 

 deposit- 

 samples 

 examined. 



Composition 

 of marine 

 deposits. 



" Challenger" Office from the British Admiralty and from many- 

 other British and foreign sources. Since the publication of the 

 " Challenger "Report, deposit-samples collected by H.M. survey- 

 ing ships and by British cable ships, as well as by many ships 

 belonging to other nations, have been forwarded to the 

 "Challenger" Laboratory for study, so that nearly all the 

 samples of deposits procured from deep water over the ocean's 

 floor have passed through our hands, and are available for the 

 preparation of maps showing the distribution of the different 

 types of deposits, and for the determination of the various 

 constituents entering into the composition of deep-sea deposits. 

 How extensive this material is may be surmised from the fact 

 that nearly 12,000 deposit-samples have been examined in the 

 " Challenger" Office. Some of these samples were very small, 

 in a few cases insufficient even to indicate the type of deposit ; 

 but the great majority sufficed for the determination of the 

 deposit-type, and of the percentage of calcium carbonate, while 

 a very large number were available for detailed study and 

 description. The samples have all been dealt with in a 

 uniform manner, the methods of examination and description 

 fully explained in the " Challenger " Report having been adopted 

 throughout, for, notwithstanding the large amount of sounding- 

 work carried on since that Report was published, the general 

 results, the classification, and the nomenclature given therein 

 have been fully substantiated and found quite adequate in every 

 respect, no new types having been discovered. 



In this place we are dealing only with deep-sea deposits, i.e. 

 those occurring in depths greater than 100 fathoms, the littoral 

 and shallow- water deposits found in depths less than 100 

 fathoms being excluded. It may be stated, however, that these 

 shallow-water and shore deposits near land are principally made 

 up of relatively gross materials directly derived from the 

 adjacent coasts, and from rivers pouring their waters and 

 detritus into the ocean. Coral sands prevail near coral reefs. 

 Volcanic sands off volcanic islands, and continental detritus near 

 the embouchures of great rivers. All these materials become 

 finer in texture with increasing distance from land, and in the 

 greater depths of the ocean. 



The constituents entering into the composition of deep-sea 

 deposits may conveniently be divided into two classes : (A) 

 those of organic origin, precipitated by organisms from the dis- 

 solved constituents of sea- water, and (B) those of inorganic 



