37 



earth of the bony lamellae, or of the ligneous fibre. These are the 

 fossilia, vulgo dicta, of Linnaeus. But since it is indubitable, that 

 the remaining principles have not only entered into intirely new 

 combinations ; but that new matter, as carbonic acid, &c. is super- 

 added, it must be allowed, that a degree of change, in the nature 

 of the substance, must have taken place. Other bodies have been 

 considered as secondary fossils, which, a slight examination will suf- 

 fice to shew, ought not to be thus classed. These are 1st. IMPRES- 

 SIONS*. These are certain hard, but once soft, mineral substances ; 

 which retain the figure which has been impressed on them, by some 

 secondary fossil. 2dly. CASTS f. These are formed by the depo- 

 sition of mineral matter in the cavities of animal or vegetable sub- 

 stances, or in the vacuities, left by the decay of organized bodies, 

 involved in some solid matrix. 3dly. INCRUSTATIONS f. These 

 are formed by such an apposition of mineral matter generally by 

 precipitation or deposition, as effects the envelopement of some 

 vegetable or animal body, in a mineral crust. 



Whatever claim to this distinction the two first mentioned of these 

 bodies may possess, from the circumstance of their actually owing 

 their form to secondary fossils, it must be, rejected ; since they 

 merely bear the form, and were themselves never endued with ve- 

 getable or animal organization. With respect to incrustations, the 

 last-mentioned of these bodies, it is sufficient to remark, that the 

 circumstance of incrustation alone, is not sufficient to constitute a 

 body, fossil ; since organic bodies, thus found, are, generally, of 

 but a late origin, and, most frequently, unaltered in their structure* 

 Due attention will, however, be paid to all these substances, when- 

 ever they serve to illustrate the actual secondary fossil ; or contri- 

 bute to the explanation of its mode of formation 



* Impressa, Linnsei ; Typolithi, Wallerii ; Type and Ectype, Breynii ; Figuratorwn 

 Lapidum Matrices, of others. 



t Rcdintegrata^ Linnaei ; Petrificata spoliata, Luidii, Noyau, Galloruna. 

 J Incrustata, 



