SKY. SOIL AND AGRICULTURE. 287 



decomposition is occasionally so complete that in many 

 places the rock, while it appears to retain its solidity 

 with its form, can be cut through with a spade, and thus 

 readily moulders into soil as soon as it is exposed to the 

 effect of the rains or to mechanical force. The chief 

 obstacle to this ultimate change must be sought in the 

 covering of peat which invests the soil. This substance, 

 scarcely pervious to moisture, prevents that access of 

 rain which, united with frost, might perfect an incipient 

 decomposition ; while, remaining for ages undisturbed, 

 it also serves to conceal that which only requires exposure 

 to become useful. An obvious improvement is thus sug- 

 gested, namely, the exposure of the subjacent rock by the 

 plough or caschrom ; which in many cases, where the peaty 

 surface is thin, is sufficient to generate at once a perma- 

 nently fertile soil by mixing the carbonaceous matter 

 of the surface with the earth that lies beneath ; a labour, 

 in most cases, sooner or later recompensed by its effect 

 in admitting the access of air and water, even where the 

 rock is not actually mouldered. Such experiments must, 

 of course, as in all other cases, be resolved into mere 

 questions of expense ; but there are few where, if that 

 can be tolerated, the certainty of the result is greater. 



Another remarkable anomaly of this nature exists in 

 the calcareous district of Strath already described, pre- 

 senting a difficulty of which there is no other apparent 

 solution. The general fertility of calcareous soils is suffi- 

 ciently notorious, and, in conformity to that rule, the 

 existence of subjacent rocks of limestone can almost 

 always be determined in the Highland mountains by the 

 patch or stripe of brilliant verdure occurring in the brown 

 waste. The district in question presents every variety 

 of elevation, exposure, and drainage; yet, with a small 

 exception occurring in the lower parts of the valley, the 

 surface is boggy, brown, and barren ; scarcely yielding 

 in poverty of vegetation to the soils that lie on quartz 

 rock, and, what is no less remarkable, almost every where 



