302 MICROSCOPIC FORMS OF VEGETABLE LIFE. 



Of their extraordinary abundance in certain parts of the ocean, 

 the best evidence is afforded by the observations of Dr. W. J. 

 Hooker upon the Diatomacese of the southern seas ; for within 

 the Antarctic Circle, they are rendered peculiarly conspicuous 

 by becoming enclosed in the newly-formed ice, and by being 

 washed up in myriads by the sea on to the " pack" and " bergs," 

 everywhere staining the white ice and snow of a pale ochreous 

 brown. A deposit of mud, chiefly consisting of the siliceous 

 loricse of Diatomacese, not less than 400 miles long and 120 miles 

 broad, was found at a depth of between 200 and 400 feet, on 

 the flanks of Victoria Land in 78 south latitude ; of the thick- 

 ness of this deposit no conjecture could be formed; but that it 

 must be continually increasing is evident, the silex of which it 

 is in a great measure composed being indestructible. A fact of 

 peculiar interest in connection with this deposit, is its extension 

 over the submarine flanks of Mount Erebus, an active volcano 

 of 12,400 feet elevation ; since a communication between the 

 ocean-waters and the bowels of a volcano, such as there are 

 other reasons for believing to be occasionally formed, would ac- 

 count for the presence of Diatomacese in volcanic ashes and 

 pumice, which was discovered by Prof. Ehrenberg. It is re- 

 marked by Dr. Hooker, that the universal presence of this in- 



Fio. 101. 



Ibssu DiatomacecB, Sec., from Oran : a, a, a, Coscinodiscus; 6,6,6, Actinocyclus ; c, Dictyochya 

 fibula; d, Lithasteriscus radiatus; e, Spongolithis acicularis ; /, /, Grammatophora parallela (side 

 view) ; g, g, Grammatophora angulosa (front view). 



visible vegetation throughout the South Polar Ocean, is a most 

 important feature ; since there is a marked deficiency, in this 

 region, of higher forms of vegetation ; and were it not for them, 



