ON THE FORMATION OF CRYSTALLINE ROCKS. 229 



snrface downwards to the point where they become predominant in 

 the depths ; that, in fine, they are in intimate connexion with all the 

 other manifestations of the internal activity of the globe, it must be 

 admitted that their study well merits the most serious attention. 



It is this study of a phenomenon, so far as it is possible for us to 

 understand it at this day, that I present in this work. I shall divide 

 it into three parts : the first will be devoted to the history of the 

 question ; the second to the exposition of those facts which can be 

 considered as certain, and which the theoretical explanations which 

 form the subject of the third part, ought to explain. 



I have given considerable development to the historical part. To 

 signalize the efforts by which the theoretical ideas which we now 

 possess have been gradually acquired, is not only to render a just 

 homage to those w^ho have illuminated science by their works, but 

 also to present a salutary warning against illusive speculations. Im- 

 pulses of the imagination in the domain of geology are so much the 

 more to be deprecated, as even the induction founded upon observa- 

 tion is here most frequently without means of verification. 



Although the historical citations are numerous, there are still many 

 gaps ; but not to too much extend this sketch, I should say that I 

 restrict myself to works of a fundamental character. 



PART FIRST. 

 HISTORY. 



CHAPTER I . 

 STATE OP GEOLOGY AT THE APPEARANCE OF THE HUTTONIAN SYSTEM. 



During the last two centuries there have been men who, without 

 being what we now call geologists, have advanced such remarkable 

 ideas concerning the system of the globe, that they have had an in- 

 contestable influence on the works of those who, since their time, 

 have specially studied this part of science. Thus Descartes considered 

 the earth as a sun cooled on its siirface, preserving in its interior a 

 central fire, which was the cause of the return of the waters of infil- 

 tration towards the surface, of the presence of metals in veins, and 

 of the dislocations of the solid crust.* 



From the same hypothesis of an original fluidity, Newton deduced 



~ The Princip'es of Philosophy of Descartes first appeared in 1644, (Latin edition of Am- 

 sterdam.) The acute genius of Descartes divined, as it were, several general facts, which 

 observation has since then established. 



" FeignoDS que cette terre a ete autrefois un astre — en sorte qu'elle ne dififerait en riea 

 du Boleil, einon qu'elle etait plus petite. Au-dessus de la croute interieure fortpesante, de 

 laquelle vieunent tous les motaux, est une autre croute de terre moins massive qui est 

 composee de pierres, d'argile, de sable et de limou. Ce n'est pas le seul argent-vif qui 

 peut amener soit les metaux de la terre interieure a I'extorieur lea esprits et les exhaliu.ona 

 font le semblable aux regards de quelques-uus, comme le cuivre, le fer et I'autimoine " — 

 (French edition of 1668, IV part, §§2, 44 and 72.) 



