FOSSIL INFUSORIA. 157 



of the shells of Infusoria ; giving a mass of animal remains amounting 

 to 22,885 cubic feet in bulk, and weighing forty tons, as the quantity 

 annually deposited there. How vast, how utterly incomprehensible, then, 

 must be the number of once living beings, whose remains have in the 

 lapse of time accumulated ! In the frigid regions of the North Pole no 

 less than sixty-eight species of the fossil Infusoria have been found. 

 The guano of the island of Ichaboe abounds with fossil Infusoria, which 

 must have first entered the stomachs of fish, then those of the sea-fowl, 

 and become ultimately deposited on the island, incrustating its surface ; 

 whence they are transported, after the lapse of centuries, to aid the 

 fruition of the earth, for the benefit of the present race of civilised 

 man. The hazy and injurious atmosphere met with off Cape Verd 

 Islands, and hundreds of miles distant from the coast of Africa, is 

 caused entirely by a brown dust, which, upon being examined micro- 

 scopically by Ehrenberg, was found chiefly to consist of the flinty shells 

 of Infusoria, and the siliceous tissue of plants : of these Infusoria, sixty- 

 four proved to belong to fresh-water species, and two were denizens of 

 the ocean. From the direction of the periodical winds, this dust is 

 reasonably supposed to be the finer portions of the sands of the desert 

 of the interior of Africa. 



The deposit of the beneficent Nile, that fertilises so large a tract of 

 country, has undergone the keen scientific scrutiny of Ehrenberg j and 

 he found the nutritive principle to consist of fossil Infusoria. So pro- 

 fusely were they diffused, that he could not detect the smallest particle 

 of the deposit that did not contain the remains of one or more of the 

 extensive but diminutive family that once revelled in all the enjoyment 

 of animal existence. It is very remarkable that at Holderness, in 

 digging out a submerged forest on the coast, numbers of fresh-water 

 fossil Diatomacese have been discovered, although the sea flows over 

 the place at every tide. 



Before entering on further details of the fossil Infusoria, we would 

 first state how they may be prepared for microscopic examination. 

 A great many of the infusorial earths may be mounted as objects with- 

 out any previous washing or preparation ; some, such as chalk, how- 

 ever, must be repeatedly washed, to deprive the Infusoria of all im- 

 purities ; whilst others, by far the most numerous class, require either 

 to be digested for a long time, or even boiled in strong nitric or hydro- 

 chloric acid, for the same purpose. Place a small portion of the earth 

 to be prepared in a test-tube, or other convenient vessel, capable of 

 bearing the heat of a lamp ; then pour upon it enough diluted hydro- 

 chloric acid to about half fill the tube. Brisk effervescence will now 



