190 Proceedings of the Royal Physical Society. 
Lower Carboniferous, and these into their minor divisions as 
shown in the following table— 
Upper Coal-Measures. 
Upper Middle Coal-Measures. 
Carboniferous. ) Lower Coal-Measures. 
Millstone Grit Series. 
Carboniferous Limestone Series of Scotland 
Lower (= Yoredale Rocks of England). 
Carboniferous. ) Calciferous Sandstone Series of Scotland 
(= Mountain Limestone of England),— 
we find that though certain species of shells extend from the 
Calciferous Sandstone Series into the Upper Coal-Measures, 
I do not know a single species of plant found in the Lower 
Carboniferous that oceurs in the Upper Carboniferous. 
So far as I have been able to ascertain, there is not in 
Britain one species common to both of these great divisions. 
Between the top of the Carboniferous Limestone Series and 
the base of the Millstone Grit, an enormous period of time 
is unrepresented by any rock in Britain—a period so great, 
that during its existence a complete change took place in 
the flora. 
But irrespective of this great break in the deposition of 
Carboniferous rocks in Britain, many of the Calciferous 
Sandstone species do not pass into the Carboniferous Lime- 
stone Series, though they have some species in common; still 
the floras of the two periods are very different as a whole. 
1 Of course Stigmaria occurs both above and below the Millstone Grit, but 
Stigmaria was the root of Lepidodendron and Sigillaria, and probably of 
Lepidophloios and Bothrodendron. All these genera occur in both the Upper 
and Lower Carboniferous rocks, but in each division are represented by 
different species. All that can be said of Stigmaria is that it is the root of one 
or other of the plants of these genera. In no case, so far as I know, can we refer 
any given Stigmaria to any given Lepidodendren, etc. All we can say is that 
the Stigmaria found in Upper Carboniferous rocks are the roots of Upper Car- 
boniferous species, and those found in Lower Carboniferous rocks are the roots 
of Lower Carboniferous species. The same remarks may be made of Lepida- 
strobus variabilis, L. and H., which is an ‘‘ aggregate species,” and of some of 
the Lepidophylli—even the named species of which evidently contain the leaves 
or bracts of more than one plant. 
