109 
Mr. Wrruerep referred to a section of the Coal-field drawn 
on a scale of sixty feet to an inch, and described the various 
divisions and floral horizons. Beginning with the Carboniferous 
Limestone, he showed that the Flora was rather Devonian than 
Carboniferous, as must be expected from the prevalence, during 
the deposition of the limestone, of Devonian land surfaces. 
At the close of the “Upper Limestone Shales” we have evidence 
that the Flora had begun to be more Carboniferous than 
Devonian. By denudation of the existing land surfaces the 
‘Millstone Grit” was gradually formed over the “ Shales.” 
In this “ grit” there are a few seams of coal, of no economical 
value—the “‘ Millstone Grit” passes gradually into the “ Lower 
Coal Measures,” and here the first workable coal-seams occur. 
Passing over the explosive gas-seams, which are not present in 
the Bristol Coal-field, the Lecturer arrived at the “ two-foot 
seam,” which is especially characterised by the presence of 
“Ulodendron Lindleyanum,” “Calanites radiatus,” and large 
“ Lepidodendron Sternberg,” together with vast quantities of 
“ Cordaites,” generally supposed to be the remains of foliage; 
but Mr. Weruerep considers that he has proved it to be a reed. 
This fossil was found to be jprevalent throughout every seam of 
coal in the coal-field of which Mr. W. had any knowledge. 
Following the lower series of coals comes the Pennant Sand- 
stone, upwards of 1800 feet thick. This formation is said to be 
restricted to the Bristol, Somerset, and South Wales coal-fields; 
but there is reason to suppose that it has been confused with 
the “Millstone Grit,” as was actually proved to be the case 
by Mr. Hanpet CossHam, in the Bristol coal-field; such mistake 
proving a serious source of error, which might be detected by 
the plant-life of the two formations, when their resemblance 
lithologically would render them otherwise undistinguishable. 
The next question was as to the nature or kind of vegetation 
of which the mass of the coal is formed. This has been popu- 
larly ascribed to large trees of Lepidodendroide or Calamite 
type, which abound in the overlying shales, but the Lecturer 
showed good reasons for believing that the coal is formed, like 
peat bogs of the present day, from reeds and mosses and plants 
I 
