DEPOSITS 



205 



the samples which contain sea water, will throw down 

 some of the sulphate of lime, in a gelatinous-like 

 condition (Bathybius), but this is not a very serious 

 objection. When a roll of the deposit is procured 

 from the sounding tube, it should be surrounded with 

 blotting paper, or pushed out on to blotting paper ; 

 the whole can then be enveloped by the paper, dried, 

 and retained for future detailed examination. The 

 colour of the sample and any other peculiarities 



Fig. 



158. — Set of Sieves for Grading the Contents of 

 Dredge or Trawl, or Material gathered on Shore 

 (" Challenger.") 



For use the whole set is immersed in a tub of sea water. 



should be carefully noted in the wet condition. A 

 label should be put on the outside of the bottle or tube 

 (not on the cork), as well as inside. 



The Depth of the Ocean. — The ocean has now been 

 sounded in nearly all directions, and our views as 

 to the relief of the sea floor are slowly becoming 

 more and more definite. It is often asserted that 

 we know very little concerning the depth of the 

 ocean, so few are the soundings compared with its 

 vast extent. It is possible to underrate the extent 



