Cornwall does not possess a great variety of rock formations, being composed of primary and transition or intermediate groups, covered here and there with deposits of gravel, sand, and clay, which belong to the modern epoch. But this limited range of formations is more than compensated for by the great facilities which the geologist here enjoys in his investigations; the very extended line of cliffs which deeply indent the Cornish shores proffer numerous and instructive sections; and the vast mining operations have brought to light most important phenomena. Indeed, no country of equal extent can, in these combined advantages, be compared with Cornwall. On a general view of this country, the surface exhibits two systems of valleys; one running parallel with the central ridge, which is highest near Launceston, and gradually, but irregularly, declines till it terminates at the Land’s End, in cliffs about a hundred feet in height; the other intersecting the longitudinal valleys at right angles; and as all the intermediate hills are more or less rounded, the country has an undulating appearance in both directions, not unaptly compared to the waves of the sea. Through these two systems of valleys, the rivers flow, seeking outlets into the sea by the nearest continuous descent; sometimes they effect this along the longitudinal, at others through the transverse valleys, receiving tributary streams on either hand from the lateral valleys, or curved hollows which they intersect. But sometimes the river is diverted in its course more than once, in consequence of the concavity of a cross curve rising above its level――or by that of the other system descending below this point――by which irregularity the stream is compelled to flow along the more favourable drainage; thus the Camel rises about four miles from the sea, in the moors near Davidstow, and flows more than twenty-five before it empties itself into the sea at Padstow. In the hollows of these valleys the drainage is often sufficiently obstructed to produce marshy ground; but seldom of such extent as to deserve the name of a lake. As regards the soil, on the high grounds it is frequently very shallow and barren; but in the valleys it is very productive, and here and there is well wooded, more particularly on the southern coast. On the northern coast, in the vicinity of the sea, it is very sandy, owing to the light testaceous sand of the shore being carried inland by high winds; in this manner no inconsiderable tracts of fertile land have been devastated.