324 Different Floras of the Rock-Formations. 
a carboniferous formation of very ancient date, since it is 
covered by beds containing fossil animals characteristic of the 
silurian formation, confirm this opinion as to the extension 
of the coal-vegetation to the commencement of the Transi- 
tion-class. In fact, I find, in a memoir by M. Sharpe, on the 
Geology of the Neighbourhood of Oporto, that pretty thick 
and numerous beds of coal, which cover slates with trilobites, 
orthites, orthocerates, graptolites, &c., contain some impres- 
sion of plants, and these impressions all of ferns, although 
somewhat imperfect, appear, according to M. Bunbury, iden- 
tical with, or very closely allied to, well-known species of 
the ordinary coal-formation. These are, Pecopteris cyathea 
and muricata, and Neuropteris tenutfolia. 
What I have said as to formations which appear more an- 
cient than the coal-formation applies equally to the red 
sandstone which covers it; the fossils, which I have seen 
from thence, differ in no respect from those of the upper 
beds of the coal-formation, properly so called. 
But if the vegetation of our globe has maintained itself 
without undergoing great changes during the whole of this 
period. it is not less certain that there have often been very 
decided changes in the species during the deposition of these 
different beds. Thus, in the same coal-basin, each bed often 
incloses some characteristic species, which are not found 
either in the more ancient or more recent beds, and which 
the miners have learned to regard as a distinctive mark of 
these beds. 
M. Graeser, at Eschweiler, has carefully observed’ this 
fact, and pointed it out tome. At St Etienne, in like man- 
ner, I have determined it in many of the beds mined in that 
basin. To give an example, I may state that the beds in 
this basin which appear to be the lowest, contain abundance 
of Odontopteris Brardii, with very large pinnules, ‘without 
a trace of any other Odontopteris; while the upper beds of 
the excavations of Treuil very frequently present’ us’ with 
Odontopteris minor, without intermixture of any other ‘spe- 
cies. In general, each bed of coal is accompanied only by 
the remains of a somewhat limited number ‘of ‘vegetables. 
Sometimes this number, particularly in the ‘most ancient 
