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bed of. compact basalt one hundred feet thick, which again is 
capped by some volcanic deposits. ‘The argillaceous strata are of 
very fine grain, and of various colours ; some portions being as 
white as chalk. Dr. Bailey has shewn that this clay is entirely 
composed of fresh-water Diatomacez. Its perfect freedom from 
sand shews that it is not a drift, but that it must have been formed 
by plants that lived on the spot. This is the largest deposit 
known. Ordinarily these deposits do not exceed from one to four 
feet in thickness ; but those of Lune-berg and Bilin have a depth 
of forty feet. Some beds are also known to attain a thickness of 
seventy feet: such are not usually pure, but are mixed with sand 
and other matters. The Island of Barbadoes contains many such 
deposits, some of which are rich in forms found nowhere else. A 
kind of stone imported from Jutland for the manufacture of cement 
is also composed in large measure of diatom-remains unlike any 
other known species. The city of New York stands on one of 
these accumulations of diatoms, having a great proportion of 
“species identical, in every particular, with the same species found 
living now in our own pools and streams. 
I will close this paper with a quotation from one of the best 
authorities on the Diatomaceze. Prof. Smith says: “Of the purposes 
served by the diffusion of these organisms, it is impossible to speak 
with certainty. Their minute size forbids us to attribute much 
effect to their individual influences ; but when we regard them as 
aggregated in numbers that defy enumeration, we are compelled 
to believe that they occupy an important place, and subserve 
necessary ends in the economy of Nature. Their nutritive process, 
which involves the absorption of Carbonic Acid and the exhalation 
of Oxygen, must tend to preserve the purity of the water in which 
they are found, and to fit it for the respiration of aquatic animals. 
Their presence in the stomachs of Infusoria, Annelida, Mollusca, 
and Crustacea, shows that they constitute to some extent the food 
of these animals; and the vast numbers of their remains which 
* occur in guano, prove that they are swallowed in large quantities 
by sea-birds, and minister to their subsistence. 
“Their direct uses to man are probably few and inappreciable, 
