Geological Society of London. 87 
for the eruption of the Dartmoor granite, and to explain why so 
much difficulty and ambiguity has prevailed in determining the age 
of some of the altered culm beds. 
Among other points which this survey of Prof. Sedgwick and Mr. 
Murchison has settled, so far as Devon is concerned, is one of the 
highest theoretical interest, and on which for more than two years 
the Society has been anxiously desiring more accurate information ; 
T allude to the true stratigrapbical position of certain shales near 
Bideford in North Devon, containing fossil plants of the same species 
as those which are found abundantly in the coal. 1 may first remind 
you that a discussion had previously arisen respecting the alledged 
discovery by Mr. Weaver of anthracite, with the usual carboniferous 
plants, in the greywacke or transition rocks of Ireland.* Notwith- 
standing the value justly attached to the opinion of so experienced 
and long-practiced an observer, your Council hesitated to print his 
statement, and requested him to reexamine the ground. At the 
same time Mr. Griffiths, to whom we are looking for the publica- 
tion of a Geological Map of Ireland, had come to a different con- 
clusion, and Mr. Weaver having been induced to repeat his obser- 
vations, became convinced that he was in error, and has since stu- 
diously availed himself of every opportunity of announcing. this 
change in his views. 
You are aware that as yet in the British islands, scarcely any ve- 
getable impressions have been met with in rocks more ancient than 
the carboniferous strata above the old red sandstone, so that we 
know not what species of plants belong to the greywacke or transi- 
tion group. We can only presume from analogy that since the 
shells, corals, and other organic remains of that ancient group differ 
from those found above the old red sandstone, the plants also, if 
ever discovered, will differ as greatly. Considerable surprise was 
therefore excited when, during the Presidentship of my predecessor 
in this chair, a letter was read, addressed to him from Mr. De la 
Beche, stating that he had found near Bideford in North Devon, 
many well known coal plants in the lower greywacke, or far down 
in the transition series.t Such of the plants as were determinable 
had been identified by Prof. Lindley with species characteristic of 
the true coal measures, and which had never been found elsewhere 
. * Proceedings Geol. Soc., vol. i. p. 231. 
+ Proceedings Geol. Soc., vol. ii. p. 106. 
