AUSTEN EXTENSION OF THE COAL-MEASURES. 57 



pbical arrangements of those times were, most of which, however, 

 mil be found indicated in the accompanying Map (PL I.), the 

 following may be taken as an outline of the geography of Western 

 Europe at that early time. 



Outline of the Geography of Western Europe at the Coal-growth 



Period. 



The central gneissic plateau of France was then a terrestrial area, 

 supporting a rich coal-vegetation, with ranges of hills which must 

 have had considerable elevation, and lines of valley of which we can 

 still determine the directions, occupied by lakes and river-courses. 

 The great linear depression of the Rhone had not then been effected. 

 This area extended S. and E., so as to be connected with the old 

 land of the Department of the Var * . Over all this tract there is to 

 be observed a remarkable uniformity in the conditions under which 

 the coal deposits have been formed, as well as in the drifted vege- 

 tation : it may be characterized as the "upland facies" of the Car- 

 boniferous period. 



The Coal-measures here occupy depressions, which were such at 

 the time of the coal-growths ; the lowest beds consist of distinct 

 subaerial detritus and alluvia, of which all the materials have been 

 derived from the slopes immediately adjacent : the coal-seams, in 

 their great depths, as compared with their extent, indicate the vast 

 periods of uninterrupted growth of Vegetable matter, and contrast 

 strongly with the frequent alternations common throughout those 

 deposits, which we know, from the subordinate beds, must have been 

 formed at the sea-level. Lastly, in the peculiar Fern-like forms 

 {Cyclopteris^ Odontopteris) which so abound in the sedimentary beds 

 and drifted sands of these basins, we have the indications, not of a 

 different period of vegetation, but merely that of the higher regions 

 of the district. Although the Coal-strata are now compressed, by 

 the contractions which have effected the whole of this old central 

 region of France, yet all these distinct features, as to the original 

 arrangements of its surface, are sufficiently distinct. This district 

 is moreover interesting, as it is one of those which ante-dates the 

 period of the carboniferous deposits, and which must have served 

 during that long lapse of time to renew the vegetation over that 

 endless succession of submerged and terrestrial surfaces which the 

 lower levels present. 



The extent of this old land must not be estimated by what has 

 been designated above as the Central gneissic plateau, as that is now 

 circumscribed by the secondary group of depositions ; because these 

 last have been brought by a process of overlap, and unconformably, 

 over these former terrestrial surfaces : nor must the present character 

 of the surface be taken as a guide as to its original inequalities ; for 



* Mem. de la Soc. Geol. de France, 2 ser. vol. iii. p. 315 ; also Explication de la 

 Carte Geologique de France, p. 470. 



