FOSSIL INFUSORIA. l33 



Darwiu, writing of Patagonia, says : " Here along the 

 coast, for hundreds of miles, we have our great tertiary for- 

 mation, 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 Pro- 

 fessor Ehrenberg has already recognized 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 thick- 

 ness 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 organization. At Richmond 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 animal- 

 cules ; for in the slightest particles of it they are discover' 

 able. On these myriads of skeletons are built the towns 

 of Richmond and Petersburg. - The species in these earths 

 are chiefly Naviculce; but the most attractive, from the 

 beauty of its form, is the Coscinodiscus, 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 

 Ehreuberg 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 com- 

 putes, 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 

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