MICROSCOPIC FOSSILS. 



000,000) forty thousand millions of distinct, organic forms. The species of Diato- 

 mucese, of which nearly the whole mass is compacted, is the divided G-allionella, or 

 box-chain organisms ; a kind of Diatomaceae which has already been described. A 

 specimen from this slate is delineated in figure 78, magnified three hundred times. 

 Its natural length does not exceed one-sixth of the thickness of a human hair, and 

 the flinty shell of a single gallionella weighs only the one 

 hundred and eighty-seven millionth part of a grain. The identity 



of the fossil and living plantules is seen at a glance by comparing 

 the engravings in which they are respectively represented. In 

 Virginia, extensive beds of flinty marls have been discovered by Professor Rogers, 

 composed, in a great measure, of the shells of different species of marine organisms. 

 The towns of Richmond and Petersburg are built upon these strata, which vary in 

 thickness from twelve to twenty-five feet, and comprise tracts and districts of con- 

 siderable extent. So full is this earth of microscopic fossil remains, that when a 

 little of it has been mixed with a drop of water, and the liquid has evaporated 

 from the glass slide, the smallest stain left upon the surface abounds with curious 

 vegetable structures, whose living types inhabit, to a great extent, the neighboring 

 seas 



In figure 79 are shown two species of Kavicula, which, with Fte- TO. 

 several others, have been recognized in the Richmond earth ; but the 

 most exquisite structure here revealed is a beautiful saucer-shaped 

 shell, the surface of which is divided into hexagonal or six-sided 

 figures, like the cells of honey-comb. The protophyte to which it 

 belongs is called, from the appearance of the shell, the Coscinodiscus* or 

 sieve-like disk: there are several species of these organisms, whose 

 shells vary in size from one-hundredth to one-thousandth of an inch in 

 diameter. 



In figure 80 is displayed a portion of the circular shell of an elegant species 

 found in the Virginia marl, which has received the name of the Fig. 80. 



Radiated coscinodiscus. It is shown very highly magnified, and 

 the rich and perfect arrangement of symmetrical forms here ex- 

 hibited, is but a faithful copy of the wondrous original. These 

 beautiful fossil shells are not confined to the Richmond locality, 

 but have been discovered in the chalk marls of Zante and Oran; 

 and Col. Fremont likewise found them in Oregon, at the Riviere 

 Aux Chuttes. The various species of this protophyte exist in a 

 living state in the sea near Cuxhaven, at the moutn of the Elbe ; 

 and the radiated coscinodiscus has also been detected in the 

 waters of the Baltic, near Wismar. 



A like deposit of microscopic shells, fifteen feet thick, exists at 

 Andover, Ct., and Ehrenberg remarks, in his memoir on the 

 Microscopic life of North and South America, "that similar beds 

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

 Labrador." 



From kokinon (Greek), a Hei*. 



