MARINE BOTANY. 



109 



brought up. The mighty ice wall which at length checked 

 the southern course of the daring seafarers, was coloured 

 brown by the Diatomacete. Floating ice, when melted, dis- 

 played them by millions. They often formed a dirty foam 

 on the surface of the Polar Sea. The Diatomacese are 

 covered with indestructible silicious husks, which explain 

 the great geological value of both these microscopical 



ISTHMIA, 



LICMOPHORA. 



creatures. Man, and all the mammals, disappear without 

 a trace ; in a short time their constituents are dissolved ; 

 while the Foraminifera and Diatomaceae construct for eter- 

 nity. Incessantly they lay their ever -increasing pavement 

 on the ocean-bed : they are ever active in throwing up sub- 

 marine mountains and banks, and filling bays and arms of 

 the sea. At the first glance, it may appear an exaggeration 

 to ascribe such an important part to beings which are so 

 small, that millions are often needed to occupy the space of 

 a cubic inch ; but when we reflect in what astounding num- 



