The straths or valleys of our larger rivers, in their passage through the alpine country, are generally {84} occupied, for several hundred feet of perpendicular altitude up the slope, by gravel, which covers the primitive strata to considerable depth, especially in the eddies of the salient angles of the hill. Every description of tree grows more luxuriantly here than in any other situation of the country; the causes of this are, _1st_, The open bottom allowing the roots to penetrate deep, without being injured by stagnant moisture; _2d_, The percolation of water down through the gravel from the superior hill; _3d_, The dryness of the surface not producing cold by evaporation, thence the ground soon heating in the spring; _4th_, The moist air of the hill refreshing and nourishing the plant during the summer heats, and compensating for the dryness of the soil; _5th_, The reverberating of the sun’s rays, between the sides of the narrow valley, thus rendering the soil comparatively warmer than the incumbent air, which is cooled by the oblique currents of the higher strata of air, occasioned by the unequal surface of the ground. This comparatively greater warmth of the ground, when aided by moisture, either in the soil or atmosphere, is greatly conducive to the luxuriancy of vegetation. _Firm dry clays and sound brown loam._—Soils well adapted for wheat and red clover, not too rich, {85} and which will bear cattle in winter, are generally congenial to the larch. _All very rough ground, particularly ravines, where the soil is neither soft sand nor too wet; also the sides of the channels of rapid rivulets._—The roots of most trees luxuriate in living or flowing water; and, where it is of salubrious quality, especially when containing a slight solution of lime, will throw themselves out a considerable distance under the stream. The reason why steep slopes, and hills whose strata are nearly perpendicular to the horizon, are so much affected by larch and other trees, is, because the moisture in such situations is in motion, and often continues dripping through the fissures throughout the whole summer. The desideratum of situation for larch, is where the roots will neither be drowned in stagnant water in winter, nor parched by drought in summer, and where the soil is free from any corrosive mineral or corrupting mouldiness. Larch, in suitable soil, sixty years planted, and seasonably thinned, will have produced double the value of what almost any other timber would have done; and from its general adaptation both for sea and land purposes, it will always command a ready sale. {86} CLASS II. SOILS AND SUBSOILS WHERE LARCH TAKES DRY ROT.