22 LOWER INVERTEBRATES. 



studied with great care. The Eozoon occurs in a serpentine limestone, in the form of 

 irregular masses of varying size up to several inches in diameter. In appearance to the 

 naked eye it consists of alternate bands of green serpentine — a silicate of magnesia — 

 and limestone, the former filling the cavities originally occupied by the sarcode, and 

 even the most minute tubuli of the nummuUne layer ; while the calcareous basis of the 

 original skeleton remains unchanged. 



The simplest, and on the whole the most satisfactory, method of studying the 

 Eozoon is to cut tolerably thin slices of the rock and place them in a very dilute acid 

 until the calcareous portion is dissolved. There then remains a perfect cast of the 

 chambers of the shell, counterparts of the original sarcode-body, even to the minute 

 tubules of the nummuline layer. We have given here the gist of the account of Drs. 

 Dawson and Carpenter, but the question of the animal nature of Eozoon is far from 

 settled ; possibly it never will be. 



In South Carohna there are immense beds of marl and limestone containing For- 

 minifera in great abundance. Prof. J. W. Bailey, in the year 1845, examined some 

 borings from a well driven through these deposits at Charleston, and also some fi-ag- 

 ments from an outcrop on Cooper River, about thirty-five mUes above that place. 

 From the borings it was observed that from one hundred and ten to more than three 

 hundred feet in depth the Polythalraia were abundant, very perfectly preserved, and 

 many of them large enough to be easily seen with a pocket-lens. Concerning these 

 tertiary deposits. Prof. Bailey remarked that they were filled with more numerous 

 and more perfect specimens of these beautiful forms than he had ever seen in chalk or 

 marl from any other locality. Similar marls are also found in Virginia, on Pamunkey 

 River, belonging to the eocene ; and in the miocene rocks of Petersburg, Foraminifera 

 are also found. 



The foraminiferal rock which underlies so large a part of South Carolina is still in 

 process of formation along the coast. The mud from Charleston harbor abounds in 

 shells of Foraminifera, and the remains of diatoms. 



Fossil Foraminifera are found in many other places in this country. They exist in 

 New Jersey, Alabama, at various points on the Missouri and Mississippi rivers, in Ten- 

 nessee, Arkansas, Noi-th Carolina, Florida, and elsewhere. The marls of certain 

 localities along the upper Missouri and Mississippi rivers are very rich in Foraminifera. 

 The latter deposit is popularly known as " prairie chalk," and the forms are different 

 from those found on the Missouri. 



In the green sands of Fort Washington, Va., Prof. BaUey made the remarkable 

 discovery that these minute and perishable organisms could be entirely destroyed by 

 chemical changes, yet leave indestructible memorials of their existence in the form of 

 mineral casts. Ehrenberg had previously observed that the lime of the shells could be 

 gradually dissolved and replaced by silica. In flints such a replacement is not un- 

 usual, and remains of shells thus mineralized can be obtained by treating the rock with 

 acid, which leaves the silicified shells intact. 



But in the green sands of the chalk formation in New Jersey, Virginia, and else- 

 where, the shells have become filled with a greenish mineral, glauconite, — a silicate of 

 iron and potash of varying composition — which has followed every contour of the 

 shell, and penetrated even the minute pores and tubuli so perfectly that the genus and 

 even the species of the Foraminifera can be readily determined by a study of the glau- 

 conite casts after the shell has been destroyed. 



The glauconite occurs in grains scattered through the green sand formation of the 



