216 Successive Geological Development. 



him in Germany, which have a structure like that of charcoal, 

 are derived entirely from coniferous timber, and Brongniart 

 gives five genera and sixteen species of ConiferjB of this 

 epoch. The Araucarian pines have large cones, and we may 

 expect to meet with the fruit of such trees hereafter, for Dr 

 Mantell tells me, he has found between forty and fifty fossil 

 fir-cones in the Wealden of England, although not one is men- 

 tioned by Dunker, in his excellent work on the Hanoverian 

 Wealden. The coal-seams of this freshwater deposit in 

 Hanover, as I had an opportunity of attesting last summer, 

 are almost exclusively made up of the needle-shaped foliage 

 of pines. 



To prevent ourselves therefore from hazarding false gener- 

 alizations, we must ever bear in mind the extreme scantiness 

 ofour present information respecting the flora of that peculiar 

 class of stations to which in the palaeozoic era the coal-mea- 

 sures probably belonged. I have stated elsewhere my con- 

 viction that the plants which produced coal were not drifted 

 from a distance, but nearly all of them grew on the spots 

 where they became fossil. They constituted the vegetation 

 of low regions, chiefly the deltas of large rivers, slightly ele- 

 vated above the level of the sea, and liable to be submerged 

 beneath the waters of an estuary or sea by the subsidence of 

 the ground to the amount of a few feet. That the areas 

 where the carboniferous deposits accumulated were low, is 

 proved not only by the occasional association of marine re- 

 mains, but by the enormous thickness of strata of shale and 

 sandstone to which the seams of coal are subordinate. The 

 coal-measures are often thousands of feet and sometimes 

 two or three miles in vertical thickness, and they imply, that 

 for an indefinite number of ages a great body of water flowed 

 continuously in one direction, carrying down towards a given 

 area the detritus of a large hydrographical basin, draining 

 some large islands or continents on the margins of which the 

 forests of the coal period grew. If this view be correct, we 

 can know little or nothing of the upland flora of the same 

 era, still less of the contemporaneous plants of the moun- 

 tainous or Alpine regions. If so, this fact may go far to 

 account for the apparent monotony of the vegetation, although 



