DIATOMS. 403 
invisible to the naked eye, they appear, when thus congregated, 
as patches of a green or brownish slimy mass, or as little glitter- 
ing tufts a line or two in height. Some of their numerous 
species are natives of fresh water, but by far the majority are 
denizens of the sea, where 
they are found from the 
equator to the poles. The 
brown scum floating upon 
the surface of the antarc- 
tic waters near the mighty 
ice barrier which arrested 
Sir James Ross’s progress 
to the south pole was 
found to consist almost 
solely of Diatomacez, and 
they are equally abundant 
in the Arctic Ocean. 
It is remarked by Dr. 
Hooker that the univer- MAYA ‘ 
sal presence of this invi- |] 
sible vegetation through- WY 
out the South Polar Seas Taeniaphora fanaa 
is a most important fea- (Highly magnified.) 
ture, since there is a marked deficiency in this region of higher 
forms of vegetation, so that without the Diatoms there 
would neither be food for aquatic animals nor (if it were 
possible for these to maintain themselves by preying on one 
another) could the ocean waters be purified of the carbonic 
acid which animal respiration would be continually imparting 
to it. Thus it is not in vain that they abound in the most 
inhospitable seas, where but for them no sea-bird would flap 
its wings, and no dolphin dart through the desert waters. 
From the indestructible nature of their flinty coverings the 
Diatoms play a no less conspicuous part in the geological his- 
tory of our globe than the calcareous Foraminifera. 
Extensive rocky strata, chains of hills, beds of marl—once de- 
posited at the bottom of the ocean, and raised by subsequent 
changes of level from the depth of the waters—contain the 
remains of these little plants in greater or less abundance. No 
country is destitute of such monuments, and in some they con- 
EE 
