222 TAI^ONTOLOGT. 



visiting-card we use in social life, we- leave with our name 

 some cretaceous Infusoria. Underlying the city of Richmond, 

 in Virginia, is an extensive bed of fossil. Infusoria, of the 

 same genera as those now living in the Northern Seas. 



It has been ascertained by Ehrenberg that accumulations 

 of these microscopic beings are choking up the harbour of 

 "Wismar, in the Baltic, and that simnar formations are 

 effecting changes in the bed of the Nile at Dongola, in 

 Nubia, and of the Elbe at Cuxhaven. 



FOEAMENIFERA. The singular organisms that form this 

 class are microscopic animals of a simple gelatinous fleshy 

 substance, without appreciable organisation, which secretes 

 a delicate calcareous many-chambered shell, of extreme 

 beauty, into the cells of which the body of the animal com- 

 pletely retires. The gelatinous . fleshy material developes 

 expansions, incessantly variable in form and completely 

 retractile into the general animal substance, and which serve 

 for swimming and for crawling. 



These beautiful little animals are alike wonderful for the 

 simplicity of their organisation, and for the variety, regu- 

 larity, and delicate structure of their shell, many of which 

 resemble those of the nautiloid molluscs. They are found 

 in great abundance on the sandy shores of warm latitudes. 



Plancus collected 6000 shells of Eoramenifera from an 

 ounce of sand from the shore of the Adriatic; and D'Orbigny 

 found 3,840,000 in the same quantity of sand from the shores 

 of the Antilles.* 



So abundant are the remains of Poramenifera, that they 

 form banks that blockade navigable channels, obstruct gulfs, 

 and fill up harbours, and, aided by the incessant labours of 

 polyps, they form at the bed of tropical seas the materials of 

 future islands. Similar operations have taken place in former 

 periods of the earth's history. Soldani t collected from less 

 than an ounce and a half of rock from the hills of Casciana, 

 in Tuscany, 10,454 shells of fossil foramenifera. Several of 

 the species are so minute that 500 weighed only a grain, and 

 others, more minute, would require double that number to 

 make the same weight. 



The calcaire grassier of France contains the shells of 



* Pictet, tom.iv.p. 214. f Saggio Orittografico, 1780, table iii. 



