have successively occupied the surface of the Earth. 77 



What I have just said of the rocks which appear more ancient 

 than the coal formation, applies equally to the red sandstone 

 which covers it. The fossils which I have seen from this forma- 

 tion do not differ at all from those of the upper layers of the 

 coal formation proper. But, if the vegetation of our globe was 

 maintained without undergoing great changes during all this 

 period of time, it is no less certain that there were often very 

 striking changes in the species during the deposit of these different 

 strata. Thus, in the same coal basin, each layer often contains 

 several characteristic species, which are not met with either in 

 more ancient or more recent strata, and which the miners have 

 recognized as distinctive marks of these layers. 



M. Grseser, of Eschweiler, has distinctly observed this fact and 

 announced it to me. At St. Etienne also I have ascertained it in 

 several of the layers worked in that basin. And, to cite an ex- 

 ample, I will add that the layers which appear the lowest in this 

 basin, contain abundance of Odontopteris Berardii, with very 

 broad pinnules, without a trace of any other Odontopteris^ while 

 the upper layers of the quarries of Treuil very frequently exhibit 

 Odontopteris, unmixed with any other species. In general each 

 layer of coal is only accompanied by the remains of a rather 

 limited number of plants. Sometimes this number is extremely 

 restricted, especially in the oldest strata, and scarcely reaches 

 eight or ten. In other cases, and more generally in the middle 

 and upper layers, the number becomes more considerable ; but I 

 think it very rarely exceeds thirty or forty species. We see that 

 each of these little local and temporary floras, which has given 

 birth to a layer of coal, is extremely limited. This is, moreover, 

 what we still see in our own times in large forests, and above all 

 in those composed of Coniferse, where one or two species of trees 

 overshadow only four or five different Phanerogamous plants and 

 a few mosses. 



But in order to discover whether these little floras, so restricted 

 in time and space, characterized so many special epochs of the 

 vegetation of the globe, it would be necessary to determine their 

 succession in several of the principal coal basins of Europe, and to 

 see if the nature of the vegetation has been modified in the 

 same manner in these different basins ; in a word, if, in the dif- 

 ferent countries, the vegetation was the same everywhere at the 

 same epoch, or was subject to local variations analogous to those 

 which render different, at the present time, the vegetation of a 

 forest of Pinus sylvestris in Germany, a forest of Abies taxifolia 

 in the Vosges, of Picea excelsa in the Jura, and Pinus Pinaster 

 in the Landes. 



I am persuaded that the study of this point, if made in a suf- 

 ficiently complete manner, would show that there are some ge- 



