4 LIFE IN THE SEA [OH. 



find them to consist of masses of Diatoms ; and almost 

 everywhere the sand would contain these though they 

 might not be visible to the naked eye. The impression 

 we should get would be that the sandy shore con- 

 tained less life than that found on the stones or 

 gravel, and this impression would probably be an 

 accurate one : nevertheless the sand would contain far 

 more life than one would at first imagine it to hold. 



As we walked out to sea to greater depths we 

 should witness many changes in the nature of the 

 sea-bottom. Here and there it would consist of bare 

 rock, or of stones and gravel, and the nature of this 

 rock or gravel would depend on that of the adjacent 

 land. But as we went further the more common 

 deposit on the bottom would be sand, although there 

 might be patches of mud, particularly in the deeper 

 parts or channels. The general arrangement would 

 be first of all rock and stones or gravels, then sands, 

 and then muds; for all these materials result from 

 the erosion of the land, and the gravel is first deposited 

 or rolled down, then the sand, and lastly the mud. 

 Out beyond a depth of about 50 fathoms the muddy 

 deposits would be more abundant than closer inshore, 

 for the finer particles of which they are composed are 

 carried for a greater distance in the water, while 

 much of the fine particles carried in suspension by 

 the water of the rivers is precipitated by the salts 

 of the sea-water and only settles down very slowly. 



