. II. RELICS. Phenomena. 9 



as it were, a part in the original fabric of the 

 globe, f 



c. No particular petrifaction is confined wholly 

 to one kind, or species of stone 



d. But, it is observable, that many species and 

 families of petrifactions are common^ in particular 

 strata, which, in others of a similar nature, and be- 

 longing to the same tract, are extremely rare.ff 



e. The substance, which forms the petrifaction, is 

 frequently of the same nature as the surrounding 

 rock. 



f. When it differs, it is always found to consist 

 of mineral matter with a finer texture, or grain, than 

 that of the matrix. 



t Hence, more intimately connected with geological researches, 

 and the various theories devised to explain the primitive state and 

 formation of the globe, than the constrvata, which usually occur 

 in modern or very modern strata. Vide III. Soil, &c. 



ft Echinitce are more common in chalk, than in other 

 calcareous strata, apparently deposited at the same period Pis- 

 cine remains are frequent in bituminous marlite, though rare in 

 common marls and limestones of the same formation. Some spe- 

 cies of shells are peculiar to compact limestone, and one (an am- 

 monite) to alluminous schistus. Another has only been found, we 

 believe, in the black, bituminous, shale accompanying our coal- 

 strata. At least, we have to observe, respecting this last mentioned 

 shell (Anomia Pecten. Linn.") that in all the specimens of it, which 

 we have collected in various parts of England, the substance in 

 question has always formed the matrix nor have we ever seen a 

 vestige of it, in any of the other argillaceous stones attendant on 

 coal. 



