Presidential Address—The Geology of Devon. 505 
Jukes-Browne, who represents the English Channel as merely a 
feature of Pleistocene geography. Doubtless the origin of the 
English Channel is a problem well worthy the attention of Devon- 
shire geologists, but at present we are considering the composition 
of Triassic pebble-beds, and must not, therefore, allow ourselves to 
be led off on a false scent. 
Mr. Pengelly’s other question, as to the origin of the porphyritic 
trap nodules, is one which embraces a far wider scope; for along 
with it must be considered the subject of igneous fragments in ‘the 
New-Red generally. One would be disposed to say that most of 
them were derived from the felspathic traps, so many of which 
make their appearance at the junction of the Carboniferous and 
New-Red. This peculiarity of position Mr. Vicary was disposed to 
attribute to the circumstance that these traps have served to arrest 
denudation in the Trias. It is said that none are to be seen in the 
coast section. Mr. Vicary regarded the earliest eruptions of this 
class of rock as having taken place between the close of the 
Carboniferous and the commencement of the Triassic, whilst the 
latest outbursts were of Triassic age. Mr. Downes also, whilst 
endeavouring to account for the presence of some Upper Devonian 
fossils in the Trias near Tiverton, has expressed his opinion that the 
hypothesis of an active volcano upon the coast of the early Triassic 
sea best meets the requirements of the case. Mr. Somervail likewise 
has expressed his views on the probable volcanic origin of the 
breccias at the base of the Trias in South Devon, and as to the 
conditions prevailing during their accumulation. 
It cannot be doubted that a careful and unprejudiced study of the 
igneous rocks in the Devonshire Trias will help to throw much light 
on an important stage in the physical history of the area. But in 
undertaking such an investigation due allowance must be made for 
the changes which the fragments have themselves undergone in 
a highly permeable formation. If lumps of hard limestone, under 
the influence of siliceous infiltration, have been converted into that 
peculiar form of orbicular silica known as “ Beekite,”’ we need not 
be surprised at felspars, derived originally from Dartmoor, having 
been converted into Murchisonite, which chemically differs from 
orthoclase mainly in containing somewhat more alumina. 
And thus it came to pass that pieces of Dartmoor granite were 
unrecognizable, whilst a generation of geologists, following De la 
Beche and Godwin-Austen, were disposed to believe that during the 
New-Red epoch, the granite of Dartmoor had not as yet reached the 
surface. Lately, speculation has taken quite a different turn. Mr. 
Worth is disposed to think that the granite of Dartmoor passed 
upwards into felsitic and volcanic rocks, remnants of which, he 
says, are to be found in the Triassic conglomerates of the county. 
Geologists, therefore, having started with the belief that the Dartmoor 
granite was covered up by sedimentaries in Triassic and pre-Triassic 
times, are now presented with a picture of a pre-Triassic volcano 
towering into the skies. It is also intimated that andesites and 
specimens of volcanic grit such as arise from the denudation of 
volcanic cones have been found in much more recent deposits. 
