SUBMARINE DEPOSITS 195 



their lives were always in a temperature of 35° F., mixed 

 up with the remains of organisms which always lived in a 

 temperature of about 80° F. This shows how difficult it 

 may be to unravel the geological records of the past, for 

 the remains of organisms which Hved under wholly different 

 conditions may be mixed together as fossils in the same 

 geological stratum. 



If we attempt to compare the submarine deposits forming 

 at the present time with those of past ages, now represented 

 by the sedimentary rocks of the geological series, it will be 

 found that while some show a close correspondence, others 

 — the deep-sea oozes — are not so obviously related to any 

 known rocks of the visible crust of the earth. 



The terrigenous deposits formed in shallow water round 

 continents and containing mineral particles such as quartz 

 grains derived from the adjacent land correspond with 

 familiar sedimentary rocks of various geological horizons. 

 Sandstone is consolidated sand; gravel of various kinds 

 may be cemented together to form conglomerates and 

 pebble-beds ; deposits of mud may be compressed into shales 

 and impure limestones. 



Similarly, the neritic deposits can be correlated with 

 various highly fossiliferous limestones, chalks and related 

 rocks in many parts of the geological series. 



The question then naturally arises — do the deep-sea 

 deposits, formed from the remains of pelagic organisms, 

 likewise become converted into any known rocks ? There 

 is no doubt that they might do so. The " Challenger " 

 dredged fragments of rock from the deep sea which were 

 found, on examination with the microscope, to be composed 

 of hardened and consoHdated pelagic deposits ; and it is 

 possible to convert Globigerina ooze, or any other pelagic 

 deposit, in the laboratory into a lump of stone which can be 

 sliced like any other rock and examined in thin sections under 

 the microscope (see Plate XII, Fig. 2) . But there is no reason 

 to believe that any rocks formed by the consolidation 



