The former of these celebrated men, by a laborious investigation of the most inaccessible districts, continued for twenty years, in which he examined the Alps on all sides, and penetrated through all their defiles; has laid open to our view the entire disorder of the primitive formations, and has distinctly traced the limits by which they are distinguished from the secondary formations. The other, taking advantage of the numerous excavations made in the most ancient mining district in the world, has fixed the laws by which the succession of the strata are regulated, pointing out the relative antiquity of these strata, and tracing each of them through all its metamorphoses. It is from him, and from him alone, that we date the commencement of real geology, in so far as concerns the mineral nature of the strata: but neither he nor Saussure have determined the fossil organic species occurring in each kind of stratum, with the accuracy which has become necessary, now that the number of animals already known is so great. Other naturalists, it is true, have examined the the fossil remains of organised bodies; they have collected and figured them by thousands, and their works will serve as so many precious collections of materials. But, considering these animals and plants more with reference to their own nature, than as connected with the theory of the earth; or regarding these petrifactions as curiosities, rather than as historical documents; or, lastly, contenting themselves with practical explanations regarding the position of each fragment, they have almost always neglected to investigate the general laws affecting the geological position of organic remains, or their connection with the strata. _Importance of Fossil Remains in Geology._ And yet, the idea of such an investigation was very natural; for it is abundantly obvious, that it is to these fossil remains alone that we owe even the commencement of a theory of the earth, and that, without them, we should perhaps never have even suspected that there had existed any successive epochs, and a series of different operations, in the formation of the globe. By them alone we are, in fact, enabled to ascertain, that the globe has not always had the same external crust; because, we are thoroughly assured, that the plants and animals must have lived at the surface before they had thus come to be buried deep beneath it. It is only by analogy that we have been enabled to extend to the primitive formations, the conclusion which is furnished directly for the secondary by the organic remains which they contain; and if there had only existed formations in which no fossil remains were inclosed, it could never have been shewn that these formations had not all been of simultaneous origin.