Page:Transactions of the Provincial Medical and Surgical Association, volume 2.djvu/78

 mineral impregnation, yet they still retain, in some degree, the confidence of the neighbouring peasantry as specifics in certain diseases, more especially of the eyes. Several natural springs are slight chalybeates, and many which are connected with mines are impregnated artificially with the salts of iron and copper. With these trifling exceptions, the whole waters of the district are remarkably free from mineral impregnation, and are, consequently, perfectly soft and delicious. So plentiful are the natural springs, that pump-water is more rarely used than in most other places.

Geology and Mineralogy.─The geological structure of a district being, in general, but remotely connected with the health of the inhabitants, I shall, in this place, content myself with a very brief outline of that of the Landsend.

The physical structure of Cornwall is very simple as far as regards the number and relation of its component rocks: it is rendered both complicated and curious, in many parts, by the vast number of its metalliferous veins.

There is every reason to believe that the central or main rock of Cornwall consists of granite, and that the interrupted chain of hills composed of this rock, which extends from Dartmoor, in Devonshire, to the Landsend, is merely the protuberant shoulders of one continuous mass.

Reposing upon this central ridge, and in general dipping from it on all sides, there is, in the language of geologists, a formation, consisting principally of varieties of clay slate, but containing subordinate strata of very different rocks. These are different