DEPOSITS OF DIATOMS 105 



by division from a single plant in one 

 month ! 



Vast numbers of these organisms are 

 peculiar to the open sea, and they possess a 

 sufficient degree of buoyancy to enable them 

 to live and to move amongst its waters with- 

 out the aid of any supporting body whatever. 

 Their buoyancy and power of movement are 

 entirely independent of the ordinary to-and- 

 fro motile power shared by them, in a greater 

 or less degree, with all the other free forms 

 of Diatomacese. 



It is impossible to conceive the extra- 

 ordinary abundance of diatoms throughout 

 the world. According to Ehrenberg, they 

 have exercised an important influence in 

 blocking up harbours and diminishing the 

 depths of channels. A mud deposit, consist- 

 ing, chiefly, of their siliceous valves, no less 

 than 400 miles long by 120 miles broad, was 

 found at a depth of between 200 and 400 feet 

 on the flanks of Victoria Land in 70 south 

 latitude. 



Deposits of diatoms are found in tertiary 



