46 M. Mohs' Summary of Geognostical Phenomena. 



rious extraordinary results have thus been produced, of which, 

 however, it is not necessary to quote any here. For it requires 

 no examples to shew, that this is not the true use which geo- 

 gnosy should have made of the undoubtedly extremely remark- 

 able phenomena of the occurrence of petrifactions in different 

 mountain-rocks. 



The following incontestible propositions, which ought never 

 to be left out of view, will render apparent the uncertainty, 

 perhaps the impossibility, of determining formations by means 

 of remains of organic beings, even supposing that the idea of 

 formations were applicable. 



1. The existence or the presence of remains of organic bodies 

 does not belong to the essential characters of mountain-masses ; 

 and it is only from such that formations or systematic determina- 

 tions can be deduced, if these are to possess a scientific value, and 

 to afford a safe application. The determination of a mountain- 

 mass remains the same, so long as that mountain-mass is not 

 altered in respect to the nature of its rock and of its relations 

 of superposition, whether it should contain petrifactions or 

 not. 



2. The species of the lower classes of animals are not yet 

 determined in such a satisfactory manner as to enable us, at 

 least in most cases, to be assured, that varieties of one and the 

 same species, which are perceptibly, but not specifically, diffe- 

 rent, are not regarded as distinct species, perhaps as distinct 

 genera. This remark is more particularly applicable to fossil 

 remains, because, in them, several of the characters are lost 

 which lead to the determination of living beings. In animals 

 provided with shells, of whose remains the most important use 

 is made, there are only separate portions, particularly the co- 

 verings, which are found fossil ; and it has been observed, that 

 very different beings of this kind inhabit entirely similar shells, 

 just as some plants of different species or genera have perfectly 

 similar leaves. Moreover, some possessors of extensive collec- 

 tions of recent and fossil shells have expected, according to 

 their own confession, that the number of species would be mul- 

 tiplied in proportion as their collections were increased ; but 

 they have found that the reverse was the case, for many of the 

 species have turned out to be varieties of one and the same 

 species, and hence have been, as it were, blended together. 



