Geological Society of London. - 89 
of the intervening epochs the testacea, zoophytes, fish and other 
classes of organic beings were several times changed. 
In regard to the proofs relied on by Mr. De la Beche, I should 
observe that he never attempted to show that the plant-bearing shales 
at Bideford were interstratified with rocks charged with sbells or 
other fossils known to belong to rocks older than the old red sand- 
stone. 
Since writing the above sketch of the different views recently pub- 
lished of the structure of Devonshire, I have received a letter from 
Mr. De la Beche, from which I am happy to learn that it is his in- 
tention before concluding his report on the Ordnance Map of De- 
von, to re-examine Devonshire. He is far, he says, from pretend- 
ing that his first views were perfect, and if he finds reason to modify 
any of them, he shall not hesitate to announce the change of opin- 
ion. In the mean time he no longer contends that the culmiferous 
strata are referable to the lower greywacke, and considers the point 
of difference to lie within a narrower compass, namely, whether the 
culm beds are to be considered as upper greywacke or coal. This 
question, on which he is not yet satisfied, evidently appears to him 
of much less theoretical importance than, I confess, it does to me. 
It is fair, however, that I should state the arguments which influ- 
ence his mind. If the plants, he says, found at Bideford in the cul- 
miferous series should belong to strata more ancient than the old red 
sandstone, the fact would not stand alone, for he has Jately received a 
letter from M. Elie de Beaumont, detailing analogous phenomena in 
Britanny. It is stated that the greywacke there closely corresponds 
in general character with that of Devon, the upper part like the 
Devonian series containing anthracite. With this anthracite or culm 
are found at Montrelais, Chatelaison, and other places, fossil plants, 
the greater part of which are identical with those in the coal meas- 
ures ; but there are others which have not hitherto been detected in 
the latter rock. Patches of true coal measures rest in unconform- 
able position upon these upper greywacke beds of Britanny. Now 
I regret that 1 have not seen any printed account of the geology of 
this part of France ; for until we learn whether the plants in question 
are associated with true Silurian fossils, the testimony is quite incom- 
plete. We know not, for instance, whether the plant-bearing series 
in question, is old red sandstone or a Silurian formation, or whether 
it is a lower part of the true carboniferous system of which the strata 
had been disturbed before a higher portion was superimposed. 
Vor. XXXIL—No. 1. 2 
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