Fully the one half of Scotland, comprehending nearly all the alpine part, consists of primary rock, chiefly micaceous schist and gneiss. These rocks are generally less decayed at the surface, better drained, and fuller of clefts and fissures containing excellent earth (especially on slopes), into which the roots of trees penetrate and receive healthy nourishment, than the other primitive and transition rocks, granite, porphyry, trap, or the secondary and tertiary formations of nearly horizontal strata, red and white sandstone, &c. Primary strata are generally well adapted for larch, except where the surface has acquired a covering of peat-moss, or received a flat diluvial bed of close wet till or soft moorish sand, or occupies a too elevated or exposed situation—the two latter exceptions only preventing the growth, not inducing rot.
Gravel, not too ferruginous, and in which water does not stagnate in winter, even though nearly bare of vegetable mould, especially on steep slopes, and where the air is not too arid, is favourable to the growth of larch. It seems to prefer the coarser gravel, though many of the stones exceed a yard solid.
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.
CLASS II. SOILS AND SUBSOILS WHERE LARCH TAKES DRY ROT.
Situations (steep slopes excepted) with cold till subsoil, nearly impervious to water.—The larch succeeds worst when moorish dead sand alone, or with admixture of peat, occupies the surface of these retentive bottoms. Where the whole soil and subsoil is one uniform, retentive, firm till, it will often reach considerable size before being attacked by the rot. When this heavy till occupies a steep slope, the larch will sometimes succeed well, owing to the more equable supply of moisture, and the water in the soil not stagnating, but gliding down the declivity.
In general, soils whose surface assumes the appearance of honeycomb in time of frost, owing to the great quantity of water imbibed by the soil, will not produce large sound larch. More than half the low country of Scotland is soil of this description.
Soft sand soil and subsoil.—Sand is still less adapted for growing larch than the tills, the plants being often destroyed by the summer’s drought before they attain size for any useful purpose: the rot also attacks earlier here than in the tills. It appears that {87} light sand, sloping considerably on moist back-lying alpine situations, covered towards the south by steep hill, will sometimes produce sound larch; whereas did the same sand occupy a dry front or lowland situation, the larch would not succeed in it. The same moist back situation that conduces to produce sound larch in light dry soils, may probably tend to promote rot in the wet. The moisture and the less evaporation of altitude diminishing the tendency to rot in dry light sand, and increasing it in wet till. Larch will sometimes succeed well in sharp dry alluvial sand left by rivulets.