156 THE MICROSCOPE. 



and it has also been discovered in Tuscany, Bohemia, Africa, Asia, 

 the South Sea Islands, and South America ; of this, almost the entire 

 mass is composed of flinty skeletons of Diatomacese. That in Tuscany 

 and Bohemia resembles pure magnesia, and consists entirely of a shell 

 called campilodiscus, about the two-hundredth of an inch in size. 



Dr. Darwin, writing of Patagonia, says : " Here along the coast, for 

 hundreds of miles, we have our great tertiary formation, including 

 many tertiary shells, all apparently extinct. The most common shell 

 is a massive gigantic oyster, sometimes a foot or more in diameter. 

 The beds composing this formation are covered by others of a peculiar 

 soft white stone, including much gypsum, and resembling chalk ; but 

 really of the nature of pumice-stone. It is highly remarkable, from its 

 being composed, to at least one-tenth of its bulk, of Infusoria ; and 

 Professor Ehrenberg has already recognised in it thirty marine forms. 

 This bed, which extends for five hundred miles along the coast, and 

 probably runs to a considerably greater distance, is more than eight 

 hundred feet in thickness at Port St. Julian." Ehrenberg discovered 

 in the rock of the volcanic island of Ascension many siliceous shells of 

 fresh-water Infusoria ; and the same indefatigable investigator found 

 that the immense oceans of sandy deserts in Africa were in great part 

 composed of the shells of animalcules. The mighty Deltas, and other 

 deposits of rivers, are also found to be filled with the remains of this 

 vast family of minute organisation. At Kichmond in Virginia, United 

 States, there is a flinty marl many miles in extent, and from twelve to 

 twenty-five feet in thickness, almost wholly composed of the shells of 

 marine animalcules ; for in the slightest particles of it they are disco- 

 verable. On these myriads of skeletons are built the towns of Rich- 

 mond and Petersburg. The species in these earths are chiefly the Navi- 

 cula ; but the most attractive, from the beauty of its form, is the Cos- 

 cinodiscus, or sieve-like disc, found alike near Cuxhaven, at the mouth 

 of the Elbe, in the Baltic, near Wismar, in the guano, and the stomachs 

 of our oysters, scallops, and other shell-fish. Another large deposit is 

 found at Andover, Connecticut; and Ehrenberg states, "that similar 

 beds occur by the river Amazon, and in great extent from Virginia to 

 Labrador." The chalk and flints of our sea-coasts are found to be 

 principally shells and animal remains. Ehrenberg computes, that in a 

 cubic inch of chalk there are the remains of a million distinct organic 

 beings. The Paris basin, one hundred and eighty miles long, and 

 averaging ninety in breadth, abounds in Infusoria and other siliceous 

 remains. Ehrenberg, on examining the immense deposit of mud at the 

 harbour of Wismar, Mecklenburg-Schwerin, found one-tenth to consist 



