TAB. LV. 



SILEX quartzum, var. arenaceuni. 



Sandstone. 



Class 2. Earths. Order l. Homogeneous. 

 Gen. 4. Silex. Spec. 1. Quartz; 



Div. 3. Amorphous. Far. 2. Graniform. 



Syn. Ferruginous Sandstones. Kiriv. v. 1. p. 365. 

 Cos colorata. Linn. Syst. Nat. ed. 1 3. v. 3. p. 64. 



Sandstones are not uncommonly impressed with the casts 

 of shells, See. They are little else than granulae of flint, 

 with iron more or less oxidated : the oxidation is most con- 

 spicuous in the crevices where the shell has been mixed 

 with a little lime, or other things, giving them different 

 tints. The shapes of many sorts of shells are found in these 

 stones, mostly Areas and Anomias. The acuminated sides 

 of the Area on the stone at the right hand seem accidentally 

 formed, from the peculiar manner of its immersion in the 

 mass. They are often found detached as figured, and serve 

 to undeceive us. These Arcse, as they surely are by the 

 length of the hinge, apparently contain many denticula- 



