78 
Now the Millstone grit contains a considerable quantity of 
iron, and the effect of this would be, as Dr. Hunt has said, very 
destructive to organic substances, and will, we think, quite 
account for the few Fossils ; for not only are the Plant remains 
scanty in the Millstone grit, but few fossils of any kind are found. 
Mr. Stoppart remarks, in the paper before referred to, that 
in one of the Brandon Hill beds a large number of Product 
are seen where the lime has totally disappeared, having been 
dissolved out, leaving a hollow mould of the shell. There is only 
one agent that could do this, namely an acid, and we have not 
far to look for that, as a great amount of carbonic acid gas would 
be generated by the destruction of vegetable matter as above 
described. The circumstances seem to suggest that the grit 
was deposited in an inland sea, or lagoon, subject to an influx of 
the ocean, by which the Fauna was introduced, but upon the 
original condition being restored, they were destroyed by the 
gases generated by decomposing vegetation. I must not, however, 
enter upon a discussion of this subject now, my only object in 
referring to it is to show that the evidence is against a climate, 
unsuitable alike to vegetation and Fauna, and its scantiness is 
not to be accounted for by anything like an interglacial period. 
The top of the Millstone grit gradually passes into the Lower 
Coal Measures, which as represented in the coalfield section, 
are between 2700 and 2800 feet thick. The lower series consists 
of more than one class of coals, and I hope to show that there 
are fossil plants characteristic of these groups, and sometimes 
of single seams of coal by which they may be determined, in 
the same way that a certain Fauna determines other strata. 
Seams of coal, and associated strata vary much in a short 
distance, and for the purpose of correlation, too much reliance 
must not be laid on the physical conditions, or on the lithology 
of the surrounding strata. 
We first come to a series of seams generating explosive gas, 
the only ones which do so in the coalfield. I regret exceed- 
ingly that my knowledge of the Flora of these seams is very 
limited, as they have as yet been worked only at collieries with 
which I have no connection. 
