1876.] 
Infusorial Earth and its Uses . 
337 
their remains are found in a single inch. Ehrenberg esti- 
mates that about 18,000 cubic feet of these siliceous 
organisms accumulate annually in the harbour of Wismar, 
in the Baltic. He has furthermore demonstrated that they 
accumulate in the beds of American and other seas, lakes, 
and rivers. 
The deep sea soundings which have lately been conducted 
in various quarters of the world, and have attracted much 
popular interest, have shown, likewise, that the impalpable 
mud or ooze which is accumulating at great depth in the 
bed of the Atlantic and other oceans is made up almost en- 
tirely of the mineral skeletons of certain extremely minute 
organisms. Of these shells, some are calcareous, and appear 
to be identical with the organisms which abound in the 
chalk of Europe — the chalk, indeed, is largely made up of 
such organic remains— while others are siliceous. One of 
these deposits in the North Atlantic has been traced over a 
distance of thirteen hundred miles in breadth, and not less 
than six hundred miles in length. 
In peat-bogs, swamps, and the like, both of modern and 
ancient origin, there are often found layers, at times many 
feet in thickness, and of considerable extent, of a white 
siliceous paste, which is found beneath the microscope to 
be made up wholly of the remains of these minute organisms. 
These deposits, with which this article is chiefly concerned, 
are designated by geologists with the name of infusorial 
earth. The substance of which they are composed has 
generally, when dry, the appearance and consistence of 
friable chalk, and the remains of which it is made up, and 
which were formerly referred to microscopic infusoria, are 
now generally held to be plants, called by naturalists diato- 
macece. The remains of these diatomaceae are of pure silex, 
and their shapes as seen beneath the microscope are various, 
and form objects often of extreme beauty. These forms are 
very marked and constant in particular genera and species, 
of which many hundreds have been described and classified 
by Ehrenberg, Bailey, and others, and while many of the 
fossil forms are identical with living species, others are 
allied to them ; and the so-called infusorial beds are some- 
times of marine and sometimes of fresh water origin. The 
infusorial earth may readily be distinguished from the several 
calcareous and clayey deposits which it resembles in appear- 
ance by the facft that it does not effervesce in acids, and its 
ready solubility in solution of caustic soda or potash. It 
has long been well known in the arts as a powder for polish- 
ing stones and metals. At Bilin, in Bohemia, which is 
VOL. vi. (n.s.) 2 1 
