Geoiogkal Map of France. S07 



posed have been formed at an epoch in which thfe 'Pei-y tfe- 

 markable animals named ammonites existed. 



The third, corresponding with the chalk foriftation, will be 

 called cretaceous rocks (terrain cretace.)* 



The name mastozootic (mastozootique) will i^eniind tis that 

 among these rocks the bones of the mammiferous quadrupeds 

 have been found, the study of which has given rise to the 

 great work that has, it may be said, created geology among 

 tis. 



The fifth group will be described by the name otpl/rdidal 

 (pyrotde), which without expressing any thing affirmaltive 

 as to the manner in which these rocks have beeti fottried, 

 will shew that they all resemble those whose igneous origin 

 is demonstrated. 



It is admitted that the best method of refpfesefiting the 

 diflFerent formations on a geological map is by different co- 

 lours, yet it must not be concealed that the existence of matiy 

 rocks in a small space, and especially their successive super- 

 positions, give rise to many difficulties; for it will be per- 

 ceived that one very importaiit formation in a country may 

 be almost constantly covered by another rock, without 

 shewing itself in a rtianner that would be represented on a 

 horizontal plane but by a very small space, or even none at 

 all. This difficulty may be avoided in special descriptions 

 by sections, which shew the interior natute of the country ; 

 but it will be seen that this method cannot be used in a map 

 of the size of that accompanying this memoir. It is there- 

 fore necessary to observe that the distinctions made on this 

 map are far from constantly shewing the eitact lirhits ; but 

 we should consider them as only shewing which is the most 



* It should be observed that in a division less adapted to the physical 

 geography of France, this small group might have been united to the 

 preceding, and that in that case the denomination of ammonean rocks 

 would have been better preserved, as ammonites still existed when the 

 chalk was formed. This denomination and that of penean rocks might 

 still be preserved when the zechstein and variegated sandstone pass into 

 the first group; for these two systems are not commonly very ricli in 

 organic remains. 



u 2 



