INFUSORIA. 17 



flour as an article of food. It consists in great part of silicious 

 shells of Infusoria, with a little organic matter. With regard 

 to the source of fossil infusorial remains in sea- water, the fol- 

 lowing evidence is given in the United States Coast Survey, 

 1856:— 



Soundings of the gulf-stream near Key Siscayne, Florida, 

 varying in depths from 147 fathoms to 205 fathoms, give a 

 light greenish-grey mud composed chiefly of Foraminifers, 

 Diatoms, Polycystics, and Geolites, in a profusion only sur- 

 passed by the fossil polycystinous strata of Barbadoes. The 

 foraminifers compose the largest part of these muds, including 

 Textularia Americana, Marginula Bachei, and other forms, 

 particularly many species of the Plicatilia of Ehrenberg, 

 which had been supposed to live only in shallower haunts. 

 The silicious shells of Diatoms abound in the residue, after 

 the calcareous foraminifers have been dissolved by acid. The 

 inorganic portion of the soundings is chiefly quartz sand, and 

 its proportion is quite small. 



Such manifestations of life, with its mineral results, have 

 been detected from the earliest sedimentary deposits to the 

 present time ; but as regards the Infusoria, they are given on 

 the grandest scale in formations of the tertiary age. The 

 town of Eichmond, in Virginia, United States, is built on 

 barren silicious strata of marine origin and tertiary age. The 

 strata are twenty feet in thickness, composed chiefly of infu- 

 sorial flint-shells, including the well-known and beautiful 

 microscopic objects, Actinoeyclus and Coscinodiscits. 



Most of the infusorial formations, as the polishing-slates 

 at Cassel, Planitz, and Bilin, are astounding monuments of 

 the operation of microscopic organisms at former periods of 

 the history of this planet. The minute size, elementary struc- 

 ture, tenacity of life, and marvellous reproductive power of 

 the Infusoria have enabled them to survive as species those 

 changes which have exterminated contemporaneous higher 



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