THE PHYSICAL CONDITIONS OF THE ABYSS 41 



deposits, for they pass gradually into one another and 

 present many intermediate forms. 



It is probable that the sea-water by virtue of the 

 free carbonic acid it contains in solution is able to 

 exert a solvent action upon the calcium carbonate 

 shells of animals as they sink to the bottom, and 

 during the long and very slow journey from the sur- 

 face to the bottom of the deepest seas these shells are 

 completely dissolved. 



The first to be dissolved would be the thin 

 delicate shells of the Pteropods and Heteropods, for 

 besides the fact that they present a wider surface to 

 the solvent action of the water they are probably in- 

 fluenced more by tide and currents, sink more slowly 

 and erratically, and thus have a longer journey to 

 perform. 



Then the smaller but more solid and compact 

 shells of the Forarninifera are dissolved, and lastly, in 

 the deepest water only the siliceous skeletons of the 

 radiolaria and diatoms are able to reach their last 

 resting place at the bottom of the ocean. 



These four oozes then are characteristic of the 

 floor of the deep oceans. In the proximity of land 

 and in inland seas where deep water occurs, other 

 muds are found differing from one another in accord- 



