Page:Transactions of the Provincial Medical and Surgical Association, volume 2.djvu/81



It has been already observed, in speaking of the soil, that the nature of the alluvial covering varies, generally, with that of the subjacent rock. It is, nevertheless, true, that at the points of junction of two rocks of different nature, as, for example, of granite and killas, the rolled stones and soil derived from one rock, are generally spread to some distance over the other. All over the country where these junctions exist, there is a belt of soil of equivocal character, to which the farmers, in some places, give the name of flux country; but it is generally found that it is the granitic or growany soil that encroaches on the killas territory, and not the killas on the granite. This is easily accounted for by the fact of the granite almost always lying higher than the killas, a circumstance which will necessarily give the direction I have noticed to any bodies moving on its surface. The extent of these encroachments is, however, remarkably small; for whenever we see a large boulder or block of granite or of greenstone, we may be pretty sure that, if not beneath our feet, rocks of this kind are near at hand.

From this brief sketch of the geological structure of this district, considered conjointly with its physiognomical character, the great dryness of the soil may be readily inferred. All the rain that falls on it, or the springs resulting from the partial accumulation and infiltration of this, are either absorbed by the friable soil, by the slaty strata, or are conveyed speedily down the declivities of the solid granite; while the short and declivous vallies, and the almost total absence of plain, afford little or no shelter for them after their descent. The exceptions already