90 



main rock by an ochraceous decomposition : on that side 

 towards the rock it is extremely porous, not unaptly resem- 

 bling French burr, which is used for mill stones c Quartz 

 or silex is not only common in our primitive mountains, 

 but also in our gravel roads. It frequently takes place -of 

 animal and vegetable substances, forming petrifactions, 

 or running, like lava or wax, into a mould, occasionally 

 passing into the state of chalcedony, cachalon, &c. Frag-> 

 ments of this specimen became opaque in burning, as did 

 that from Scotland. Crystals of specimens nearly dode- 

 caedral on Lancashire and Bristol iron ore are properly rock; 

 or mountain crystal, as they burn transparent. 



