APPENDIX. 421 



durated clay, and are not petrified, having the shells 

 complete, and in some instances the impressions only re- 

 main, the shell having been decomposed. ^ 



The arc shell is found in the Mediterranean and the 

 West-Indies, and not on our coast. I have compared 

 them with the recent shells in my cabinet from the Me- 

 diterranean, and they correspond in external figure. 



It is worthy of remark, that almost all shells imbedded 

 in clay, are not petrified ; but indurated ; having the ap^ 

 pearance of having been submitted to the action of fire, 

 or calcined ; and are properly denominated Conservata. 



Pectinlte, 



A variety called by Linnaeus Nodosa, very large, 5 to 

 6 inches in diameter, with the Tintinnabuhim attached in 

 considerable number to the surface, of about an inch in 

 length ; these are converted into sandstone, and found in 

 James's river, State of Virginia ; these are generally 

 equivalve; the hinge lies on a straight line, like the Es- 

 callop, but set with several parallel and straight ridges, 

 and furrows, 



I have specimens also from the Counties of Columbia, 

 Rockland, West Chester, and New- York. Those from 

 Columbia and West Chester are imbedded in carbonate 

 of lime ; those from Rockland and New- York, in clay. 



The mass of Pectinites I found on a mountain in Rock- 

 land, are much water-worn externally. Those found 

 on the island of New-York, were discovered near the 

 State Prison in digging down a hill. 



I have also a singular aggregated mass of shells, com- 



