Geological Map of France. 303 



These rocks are so intimately connected with the primor- 

 dial rocks, that it is often very difficult to trace the line 

 of demarcation, and it is very remarkable that this union 

 takes place equally with all the systems of primordial rocks. 

 It results from tliis circumstance, that, always partaking of 

 the nature and even the colour of the primordial rocks, that 

 they immediately follow, they present the greatest differences 

 with each other. Thus for example, if they succeed red 

 granite, they are also red, and contain much felspar; if 

 they follow talcose rocks, they are greenish grey, and of 

 a composition analogous to that of these rocks. It even 

 appears that in some countries, and especially in some can- 

 tons of the Alps^ this formation is represented by calcareous 

 beds interposed between two formations also calcareous, the 

 separation of which they mark, and from which they are 

 only distinguished by slight differenees in texture and co- 

 lour; hence there is considerable difficulty in distinguish- 

 ing the secondary and transition rocks of this country. 



Another character of the rocks forming the group that at 

 present occupies us, is, that they contain a great quantity of 

 conglomerate (clastoide), and arenaceous rocks, i. e. com- 

 posed of fragments or grains of greater or less size, and of a 

 more or less different nature ; yet this texture does not be- 

 long exclusively to this formation, it is on the contrary 

 found in almost all formations ; it may even be said that 

 we rarely pass from one formation to another without ob- 

 serving some beds which have this peculiar texture, but at 

 no epoch have these rocks been so abundant or so general as 

 this. Does not this shew that this epoch is one of the most 

 remarkable presented in the study of the globe, and conse- 

 quently that the division above proposed is one of the most 

 natural ? 



has placed the coal measures partly in the primordial rocks and partly 

 in his first secondary group, as he thus makes two things of that which 

 is essentially but one; the coal measures of the Pays Bas are precisely 

 the same as the English, and the transition rocks (according to the au- 

 thor) with which they are connected are our carboaiferous limestones 

 and old red sandstone. 



