Geological Map of France. 301 



the Montagne Noire, and the Alps, is distinguished by a 

 great quantity of slaty rocks containing more or less talc. 



We are lastly, in the intermediate space, struck with the 

 abundance of granite in the primordial rocks of the centre 

 of France, the Vosges, the Foret Noire, &c. 



Yet I renounced the desire I had of making these dis- 

 tinctions on the map, because in the present state of my 

 knowledge, I could attach no geological consideration to it, 

 and because these distinctions might arise solely from cer- 

 tain systems of rocks, common to the three bands, being 

 more developed in one than in the other. 



In fact, if I were desirous of finding the most ancient of 

 these three modifications, I should direct my attention to 

 •the summits of the Alps and Pyrenees, which have long been 

 regarded as the crests of the ancient world ; but I see, that 

 M. Charpentier,* considers the granite of the Pyrenees 

 less ancient than that of Saxony ; that M. von Buch + be- 

 lieves that the granite of St. Gothard rests on talcose and 

 calcareous rocks ; and I observe that the granitic rocks of 

 Mont Blanc bear great analogies to those in the Tarentaise, 

 which M. Brochant has shewn | to belong to the transition 

 series. If I afterwards descend into the centre of France, 

 to exiimine a granite altogether similar to the rocks of 

 Saxony, which are regarded as of the most ancient formation, 

 I remark considerable resemblance to the rocks which, in 

 Britanny and the Contentin, rest, as in Norway, on transi- 

 tion rocks, and an intimate connexion with the secondary 

 rocks evidently posterior to the transition series. 



On the other hand, the union into a single group of all 

 the primordial rocks, i. e. of those commonly called primi- 

 tive and intermediate, has presented the most fortunate 

 harmony with the physical and economical considerations 

 that may be deduced from the work which forms the sub- 

 ject of this memoir; for nearly, with the exceptions that re- 

 sult from the mineralogical nature of some particular rocks, 



• Journal des Mines, t. xxxiii. p. 101. 



+ Leonhard's Taschenbuch, &c. ; 6. Jahrgang, seite 335. 



:|: Journal des Mines, t. xxiii. p. 322. 



