486 
JOURNAL OF THE PLYMOUTH INSTITUTION. 
industries. The peninsular form of the two counties, presenting a 
very extensive coast line, provided with many harbours either 
already possessing great facilities of access or capable of being 
rendered so, at a moderate expenditure of capital, is very striking, 
and remarkably well adapted for the development of their mineral 
resources. 
The most remarkable geological features of the two counties are 
observable in the prevalence of extensive granitic ranges of hills of 
moderate height, with their concomitant phenomena of metalliferous 
deposits. 
These, studied in the light of the recent Challenger deep-sea 
investigations, tend to show that the whole district, comprehending 
the coralline limestones, the Devonian sandstones, and the meta- 
morphic rocks, has been elevated from the ocean depths by the 
granitoid eruptive rocks, which have helped to bring to surface the 
metalliferous stores which constitute the main object of the wealth- 
seekers. 
Of the origin of the limestone rocks we can have no doubt, for 
we have the remains of their coralline builders still with us ; and 
although they are now in open air, and not in ocean depth, we 
are as certain of their history as if their construction had proceeded 
immediately under our own cognizance. 
The subjacent slate rocks, we now have reason to believe, were 
derived from palaeozoic remains, although their life-origin* is not 
so clearly written upon them ; but the question is suggested 
whether they may not have an intermediate, but now missing 
link, the chalk formation at present represented by the more 
recent coral limestone. 
The positions of the soft slates, and of the hardened metamor- 
phic rocks, as well as their composition and constitution, are in 
accordance with the exhibition of forces clearly indicated by the 
appearance of the granitoid and other eruptive rocks, and give at 
least very strong evidence in favour of the theory that great forces 
from below have thrust up the granitic ranges, and have opeued 
such communications with metalliferous sources at great depths 
below the earth's surface as have rendered them available to 
human research. 
The practical miner everywhere in the two counties recognizes 
the fact, that at the junction of the granite and the killas are the 
localities where lodes or metalliferous deposits are to be sought 
