FOSSIL DIATOMACE. 89 
‘water, by some unknown process, and their tissues are com- 
posed of pure quartz; hence, under the microscope, their 
remains, consisting wholly of rock crystal, exhibit the most 
exquisite forms, elaborately fretted and ornamented (see 
Lign.4). After the death and decomposition of these plants, 
their durable frustules or cases appear as colourless discs, 
cups, spheres, shields, &c., and these accumulate at the 
bottom of the water in such inconceivable numbers, as to 
form strata of great thickness and extent. Slowly, imper- 
ceptibly, and incessantly, are the vital energies of these 
atoms separating from the element in which they live the 
most refractory and enduring of mineral substances, silex, 
and elaborating it into imperishable structures, and thus 
adding enormous contributions to the accumulations of 
detritus, which make up the sedimentary rocks of the crust 
of the globe. 
The extent of this infinitesimal flora throughout regions 
where no other forms of vegetation are known, is strikingly 
demonstrated by the observations of our eminent botanical 
traveller, Dr. Joseph Hooker, in his account of the Antarctic 
regions. * 
“ Everywhere,” Dr. Hooker states, “the waters and the 
ice alike abound in these microscopic vegetables. Though 
too small to be visible to the unassisted eye, their aggre- 
gated masses stained the iceberg and pack-ice wherever the 
latter were washed by the sea, and imparted a pale ochreous 
colour to the ice. From the south of the belt of ice which 
encircles the globe, to the highest latitudes reached by man, 
this vegetation is everywhere conspicuous, from the contrast 
between its colour and that of the white snow and ice in 
which it is imbedded. 
“ In the 80° of south latitude all the surface ice carried 
along by currents, and the sides of every berg, and the 
* “On the Botany of the South Polar Regions;” in Sir J. Ross’s 
Voyage of Discovery. 
