1 {') PALAEONTOLOGY 



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, Actinocyclus and Coscinodiscus. 



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 

 destroying causes which have exterminated contemporaneous 

 higher forms of organism. Species of Bacillaria still exist 

 which were in being at the period of the deposition of the 

 chalk. Existing species of Diatomacccc have been detected 

 as low down as the oolite. The discovery by Ehrenberg 

 of more than twenty species of silicious-shelled Infusoria, 

 fossil, in the chalk and chalk-marls, which are identical in 

 species with some now living in the lied of the Baltic, is an 

 instructive addition to the obscure history of the introduction 

 of species of living things in this planet, and must add greatly 

 to the interest of the infusoria] class in the eyes of the geo- 

 logist and philosopher. "For these organisms," writes Khren- 

 berg, "constitute a chain which, though in the individual link 

 it lie microscopic, ye1 in the mass is a mighty one, connecting 



