Geological Map of France. 305 



and that it almost always passes into the coal measures or the 

 marly rocks, which are probably the representatives of the 

 variegated sandstone, a system which is also very slightly 

 developed in these countries. It may be useful to remark 

 here that the rocks placed in this group offer, in France, one 

 remarkable circumstance; which is that the beds on the 

 north of the Juia and the Cevennes are nearly horizontal, 

 whilst those that occur in the Jura, the Alps, the Cevennes, 

 and the Pyrenees, have constantly an inclination which may 

 be expressed by the term arqure (arched, saddle-shaped) : 

 this difference would appear to be independent of the epochs 

 of formations : it may however possibly arise from the former 

 constituting hills, and the latter elevated mountains. 



The chalk formation, such as I have determined it in a 

 preceding memoir, i. e. comprising the tuffas, sands, and 

 marls, which occur beneath the true chalk, ccnstitates the 

 third group. 



It must be confessed that this formation, considered in a 

 purely geological manner, is not of more importance than 

 many of those which I have noticed in the preceding group ; 

 but I considered that it should be distinguished on the map, 

 on account of the extent it occupies in France and the Pays 

 Bas, where it forms gulfs in the midst of more ancient rocks, 

 and is distinguished from the neighbouring countries by 

 peculiar physical proj^erties. 



I unite in the fourth group all the rocks posterior to the 

 chalk, whose aqueous origin is not doubted. These rocks, 

 which were but little known a few years since, occur almost 

 every where, and their history now forms one of the most 

 important parts of geology. Their number and the differ- 

 ences they present, would demand a subdivision, if their 

 frequent superpositions would not render these details im- 

 possible in a general map. 



These rocks are distinguished moreover in the different 

 countries where they exist by remarkable differences, arising 

 from certain systems being more developed in one place than 

 another; thus in the north of Germany and the Pays Bas, 

 they form sandy plains, which mix with the sands of the 



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