MINUTE ORGANISMS. 141 
tions in both the living and the inanimate kingdoms of nature. 
Of the offices assigned to these creatures, the most familiar to 
common observation is the extraction of lime, and, more rarely, 
of silex, from the waters inhabited by them, and the deposit of 
these minerals in a solid form, either as the material of their 
habitations or as the exuvize of their bodies. The microscope 
and other means of scientific observation assure us that the 
chalk-beds of England and of France, the coral reefs of marine 
waters in warm climates, vast calcareous and silicious deposits 
in the sea and in many fresh-water ponds, the common polish- 
ing earths and slates, and many species of apparently dense and 
solid rock, are the work of the humble organisms of which I 
speak, often, indeed, of animalculze so small as to become visi- 
ble only by the aid of lenses magnifying thousands of times the 
linear measures. It is popularly supposed that animaleule, or 
what are commonly embraced under the vague name of infuso- 
ria, inhabit the water alone, but naturalists have long known 
that the atmospheric dust transported by every wind and depos- 
ited by every calm is full of microscopic life or of its relics. 
The soil on which the city of Berlin stands, contains, at the 
depth of ten or fifteen feet below the surface, living elaborators 
of silex;* and a microscopic examination of a handful of earth 
connected with the material evidences of guilt has enabled the 
naturalist to point out the very spot where a crime was com- 
mitted. It has been computed that one-sixth part of the solid 
inatter let fall by great rivers at their outlets consists of still 
recognizable infusory shells and shields, and, as the friction of 
rolling water must reduce many of these fragile structures to a 
state of comminution which even the microscope cannot resolve 
into distinet particles and identify as relics of animal or 
of vegetable life, we must conclude that a considerably larger 
proportion of river deposits is really the product of animal- 
cules.t 
* WirttweR, Physikalische Geographic, p. 142. 
+ To vary the phrase, I make occasional use of antmaleule, which, as a popu- 
lar designation, embraces all microscopic organisms, The name is founded 
