Correspondence—Mr. W. W. Watts. 335 
Daubeny in his Reports to the British Association 1847—1850, 
“On the Influence of Carbonic Acid Gas on the Health of Plants, 
especially to those allied to two Fossil Remains found in the Coal- 
formation.” These, although wanting in definite measures and not 
embracing the whole field of inquiry, are of great value so far as 
they go, as they confirm at all events the possibility of the original 
suggestion of Brongniart with respect to the condition of the atmo- 
sphere during the Goal Period. 
Daubeny showed that Lycopodium continued during five weeks in 
perfect health in an atmosphere containing 5 per cent. of carbonic 
acid, though species of Adiantum appeared less thriving than the 
corresponding plants not so treated, but that 20 per cent. of carbonic 
acid proved injurious in two or three days. He also found that 
Frogs and Newts did not appear to suffer in an atmosphere containing 
5 per cent. of the gas. This, however, is a proportion quite excessive 
and perfectly unnecessary for the object in view, and is therefore 
beyond the mark. Nevertheless, Daubeny came to the conclusion 
that the general tenor of his experiments justified him ‘in inferring 
that there is nothing in the organization of those plants and animals 
of the present day which appear most nearly allied to such as were 
in existence during the Carboniferous epoch, or even somewhat 
subsequent to that period, militating against the probability, that a 
larger amount of carbonic acid may have been present in the atmo- 
sphere and diffused throughout the waters of the sea and rivers, than 
is found either in the one or the other at the present time; nor is 
there anything to prevent us from imagining that the absorption of 
carbon by vegetables and the consequent rapidity of their growth 
may, at least within certain limits, have borne some proportion to the 
greater amount of carbonic acid assumed to have been present at 
earlier periods in the history of our globe.” 
JosEPH PRESTWICH. 
THE GEOLOGY OF MYNYDD MAWR. 
Sir,—I have been much interested in Mr. Harker’s description of 
the rocks of Mynydd Mawr and the Nantlle Valley. His observations 
on the cleavage structure round the intrusion point it out as a great 
“eye,” whose main axis runs parallel to the cleavage of the district. 
Last year, while endeavouring to work out the structural relations 
of the mass, I paid considerable attention to all the junctions, especially 
those along the §.H. flank. These are everywhere of an obviously 
intrusive character, the ‘“‘ quartz-porphyry ” frequently transgressing 
upon the bedding of the slates. The main difficulty about the junction 
to me was that in some places the slates dipped under the intrusive 
mass, while in others they dipped off it. But I found one section in 
which the bedding rose vertically, and then bent outwards at an angle 
of 45°, the porphyry in the upper part resting on the slate. Probably 
this relation of the two rocks frequently exists round the hill, the 
lines of rock flowing (if we may use the term) round the intrusion 
not only in a horizontal but also in a vertical direction. 
University Museum, Oxrorp. W. W. Warts. 
