Fossil Organic Remains. 45 



But this constancy is hot universal, but is confined to indivi- 

 dual, often very extensive, basins, which separate the moun- 

 tainous tracts from one another, and consist of those plains 

 which extend between them ; and it sometimes also undergoes 

 modifications even in these. It is possible that in neigh- 

 bouring, or even in widely separated, basins, one kind of se- 

 quence may prevail in the there formed mountain-rocks, but 

 experience teaches us, that, even in adjoining districts of this 

 kind, this sequence is more or less different ; and it will be 

 found to present even greater differences in this respect as our 

 knowledge of it becomes more extended, and when the eager- 

 ness to find again in other tracts, what had been found in the 

 normal ones, shall have lost its influence on observations. This 

 eagerness has produced a mode of reconciling the discrepancies, 

 and of establishing a general agreement of formations, of which 

 it is necessary to say something in this place, because a re- 

 gard to it, in the search for useful minerals, can be as useful 

 on the one hand, as it can be hurtful on the other. I allude 

 to the application of the remains of organic beings, i. e. petri- 

 factions of the animal and vegetable kingdoms, to the deter- 

 mination of formations, or generally of the rocky masses, con- 

 stituting the so-called secondary rocks. 



Estimate of the value of Petrifactions or Fossil Organic re- 

 mains in the determination of Rock-formations. — The difficulty 

 of determining the formations of the secondary series from 

 purely geognostical characters or relations, has introduced 

 the necessity of taking petrifactions into consideration, in or- 

 der to remove it. But the agreement of the relations of the 

 rocks and of superposition, with the phenomena of the fossil 

 remains of organic bodies, has, in many instances, been found 

 to be so slight, and so many important contradictions be- 

 tween the two have been signalised, that conclusions have 

 thence""' been deduced respecting the deceptive nature of mine- 

 ralogical and geognostical characters (not their deficiency and 

 imperfection) ; and at last, in such determinations, the nature 

 of the rock, and the position of the masses, have been entirely 

 thrown aside, and recourse has been had solely to petrifactions, 

 and the field of geognosy has thus been entirely forsaken. Va- 



* Bulletin de la So< \et6 Geologiqne de France. 



