BRITISH ASSOCIATION. 
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present time; and Mr. Hopkins believed it would be found 
equally so with all tlie observed phenomena of that region. 
On the Granite and other Volcanic Rocks of Lundy Island^ by 
the Rev. D. Williams, F.G.S. 
Mr. "Williams described this island as a mass of grey granite, 
three miles long by about half a mile wide, flanked at its S.E. 
angle by slate rocks, which beyond the immediate influence of 
the granite, had an E. and W. strike, and extended for about 
half a mile. The circumstances attending the granite were al- 
together unlike those of any granite mass of Devon or Cornwall. 
The usually abundant evidences of the processes by which the 
bounding rocks had been reduced and converted into granite in 
the vast volcanic laboratories, were all absent. He could not dis- 
cover a vestige of a granite vein, nor could he observe any where 
a trace of gneis, mica, or chiastohte slate. In Devon and Com- . 
wall, he had often observed that the mineral characters of granite, 
especially in the veins, varied with the lithological constitution 
of the sedimentary or other rocks, out of which it had been de- 
rived, and with which it was so intimately associated. Besides, 
the incorporation, the welding, as it were, of the granite in veins 
w^ith the sedimentary rock, was commonly so perfect that it was 
altogether impossible to separate them. Now at Lundy Island, 
although he had repeatedly tried at several visits, he never had 
succeeded in detaching a specimen of slate united with either 
the granite, trap, or porphyry, though it was considerably in- 
durated and altered by them, and otherwise in precisely the 
same condition as the slates in Cornwall. He proposed, in re- 
ference to the agency of heat on rocks contiguous to igneous 
masses, to distinguish between active and inert heat — the former 
exerted in reducing the minerals to fluids, the latter simply in- 
durating and otherwise partially altering them. The junctions 
of the slate and granite at Lundy, which were very clearly ex- 
posed on the N.E. and the S.W. evidenced nothing more than 
the operation of inert heat : the granite there was manifestly 
