94 Wr Production and Generation 



We are next to examine thofe periwinkle and 

 mufcle fhells, either quite penetrated, or crufted 

 over by the pyrites \ and fome of thefe fhells have 

 their whole cavity lined therewith, as the belem* 

 nites \ others, together with the pyrites, hold a fe- 

 Jenitical matter, or gypfum-ftone j again, in others, 

 the fhell is entirely pyrites ; again, the pyrites is 

 externally weathered on the periwinkle or mufcle 

 figure, which is commonly a marl, or gypfum- 

 ftone, fometimes at one, fometimes at the other end, 

 and fometimes all over it 5 and, which is the rareft 

 cafe, the fhell (till remaining, the pyrites lies imme- 

 diately either on, under, or between the fhell. Now 

 though periwinkles and mufcles are in fuch quan- 

 tities in nature, the number thus petrified is hitherto 

 found inconfiderable ; but the famples I have either 

 in my own pofTeflion, or have feen, or been told 

 of, are moftly cornua ammonis, telling, chama, aftroi- 

 ta, belemnita, turbines, peftinita, fungita, alveolus, 

 Luidii, &c. Though 'tis not to be doubted, but time 

 may difcover more forts ; nay, that the fame may be 

 prefumed of all fuch as lie in earths, where nature 

 finds materials, opportunity, juices, free accefs, 

 and the like circumftances, as grounds and founda- 

 tions for a pyritijication ; for, both mufcle and peri- 

 winkle works are all, in the ground of their earthy 

 mixtion, one and the fame, namely, already fuch 

 in nature as that, among all the parts of animals, 

 nothing comes nearer to the (tones of the mineral 

 kingdom, efpecially the calcarious fort} confequent- 

 ly that they are fitted, almoft in their native (late, 

 or at lead without any peculiar tedious preparation, 

 barely by means of a (lender exficcation, both for a 

 proper petrification, and the conception of ore, is 

 not repugnant to my hypothecs. And thus it de- 

 pends on the abovementioned circumftances, that 

 fuch (hells are, at fome times, now found changed 5 



at 



