,8,, DEEP-SEA DEPOSITS. 25 



the remains of radiolaria and sponges may also be present. When 

 wet, it has a yellowish straw or cream colour ; when dry it resembles 

 flour. This deposit was found by the " Challenger" in the Southern 

 Ocean only, and within the limits of the Antarctic ice-drift. The 

 mineralogical and petrological constituents are accordingly much 

 more varied than is the case with the previously described deposits. 

 Fragments of granite, micaceous sandstone, amphibolite, gneiss, 

 schists, and slate have been found, together with such minerals as 

 might be derived from these rocks. The ubiquitous volcanic rocks 

 and minerals are also present. Diatom ooze has been found by the 

 •' Tuscarora " in the northern part of the Pacific Ocean. 



The term globigerina ooze has been applied by the authors to 

 those deposits which contain over 30 per cent, of carbonate of lime, 

 principally due to the shells of pelagic foraminifera belonging to the 

 genera Globigerina, Orbulina, and Pulvinulina. Bottom-living forami- 

 nifera, such as those belonging to the Textulariidae, Miliolidae, and 

 Nummulinidae, may also be present, but not to any great extent. 

 Shells of the pelagic mollusca are frequently found. In regions far 

 removed from land, particles of volcanic glass and the minerals 

 felspar, augite, and hornblende are found, without any admixture of 

 land detritus ; but where the globigerina ooze approaches land and 

 merges into the terrigenous deposits, a considerable amount of such 

 detritus is present. 118 samples are classed as globigerina ooze; 

 they come from depths ranging from 400 to 2,925 fathoms. Pteropod 

 ooze differs from globigerina ooze only in the greater abundance of 

 pteropod and heteropod shells. It is found in shallower water than 

 the typical globigerina ooze, and is known only in the Atlantic. In 

 the following table, column I. represents the average composition of 

 red clay; column II. that of radiolarian ooze, and column III. that 

 of globigerina ooze : — 



Carbonate 

 of lime 



Residue 



The percentage composition of each of the deposits is given in 

 the same way ; so that an enormous amount of labour must have 

 been expended in the preparation of this Report. 



We come now to the terrigenous deposits. Of these, blue mud 

 is the most widely distributed. The upper layer is red or brown, 

 owing to the presence of ferric- oxide or ferric hydrate. Only the 

 lower portions show the characteristic colour. In these, a reduction 



