in a neighbourhood, with a view to trace the variations in its soils according to the change of the substrata. The essay to which we allude, is a paper published in the first volume of the Transactions of the Royal Geological Society, entitled, "Observations on the Geological Structure of Cornwall, with a view to trace its connection with, and influence upon its agricultural economy, and to establish a rational system of improvement by the scientific application of mineral manure." We shall extract some passages from this paper, in order to confirm the assertion made in the text. "There is certainly no district in the British empire where the natural relations between the varieties of soil and the subjacent rocks can be more easily discovered and traced, or more effectually investigated, than in the county of Cornwall; and no where can the information, which such an enquiry is calculated to afford, be more immediately and successfully applied for the improvement of waste lands, and the general advancement of agricultural science.

"As we advance from a primitive to an alluvial district, the relations to which I have alluded become gradually less distinct and apparent, and are ultimately lost in the confused complication of the soil itself, and in that general obscurity which necessarily envelopes every object in a state of decomposition: we can, therefore, only hope to succeed in such an investigation by a patient and laborious examination of a primitive country, after which we may be enabled to extend our enquiries with advantage through those districts which are more completely covered with soil, and obscured by luxuriant vegetation; as the eye gazing upon a beautiful statue, traces the outline of the

limbs, and the swelling contour of its form, through the flowing draperies which invest it. The county of Cornwall may be said to consist of four primary rocks, each of which, by decomposition, gives origin to a peculiar soil, distinct in its nature and characters, and requiring an appropriate system of cultivation and improvement. They all, however, agree in one essential particular, their earthy combinations are few and simple; the great object of art, therefore, is to extend and multiply them, and thereby to increase and diversify their chemical and mechanical agencies. In alluvial districts the very contrary obtains, for nature has already mixed and compounded the different particles of rocks in every proportion, and in every manner, and has therefore left but little to be effected by the suggestions of science, or the resources of art. The principal rocks of which Cornwall consists are granite, slate, hornblende rocks, and serpentine. Beds of limestones, dykes of porphyry, veins of quartz, and those of other minerals, will also claim a portion of our attention, inasmuch as they produce an influence upon the soils beneath which they occur.

"Granite forms the skeleton of the county, upon which all the other formations repose; the soil to which its disintegration gives origin, is provincially termed a growan soil; it occupies a very considerable area of the peninsula of Cornwall, constituting not less than 300,000 acres, one half of which is uninclosed waste land, affording a scanty pasturage for a miserable breed of sheep and goats; but which, by drainage and judicious cultivation, might, without doubt, be much improved. The other portion of growan land is endowed with various degrees of fertility

and capability of improvement, in different districts, or even in different spots in the same district; a fact which seems to have an immediate connection with the nature of the granitic substratum, and consequently to admit of elucidation from the enquiries of the geologist. That the texture of granite, and the proportion of its component parts, have a considerable influence upon the fertility of the superincumbent soil, will become evident on a bare inspection of specimens brought from fertile and barren districts. Mr. Tyacke, of Godolphin, has furnished the society with some striking specimens in confirmation of this fact, and others equally satisfactory and conclusive have been added by Mr. Giddy, the active curator of the museum. It is hardly necessary to remark, that granite consists of three substances in the state of mechanical admixture, viz. felspar, mica, and quartz, the first and last of which being essentially different in chemical composition, are necessarily so in their agricultural influence. Felspar is capable of being, in part, resolved into aluminous earth, and includes, moreover, several elements which have been discovered by experience to be highly congenial to the process of vegetation; quartz, on the contrary, has a powerful tendency to resist disintegration, and, even when it is decomposed, is reduced only into siliceous particles. The nature of felspar varies also very considerably in different kinds of granite; it occurs sometimes in an earthy form, is easily pulverized, and emits, when breathed upon, a strong smell of aluminous earth; at other times, it is met with in a hard, compact, and less earthy state, not easily yielding to the action of air and moisture. In some felspar the proportion of its siliceous greatly exceeds that of its

aluminous elements, and in others, again, magnesia forms a constituent part. The relative proportion of mica appears also to have some influence, and where this ingredient occurs in considerable quantities, it is generally indicative of a poor and light soil. There are, besides, incidental ingredients in granite which must be taken into account, such, for instance, as iron, whose presence not only disposes the rock to a more rapid decomposition, but frequently becomes a useful element in the resulting soil. It would appear, then, from these views, that the value of a growan soil will bear a relation to the proportion of felspar in the subjacent granite; it is, therefore, a circumstance which should always be examined by the scientific agriculturist, who wishes to form a correct estimate of the capabilities of any granite district. Upon an examination of many of the more fertile parts of Cornwall, this fact is very strikingly exemplified; it will be found, that in such districts the quantity of felspar in the granite varies from 70 to 90 per cent.; and that it possesses also the earthy texture which so greatly accelerates its decomposition; this is one of the mineralogical circumstances which will explain the unusual fertility of Saint Burian, Sennan, and Saint Levan, near the Land's End; the lands of which are let, upon an average, at the rent of four pounds per acre. On the other hand, let the geologist, on passing over the dreary and barren moors which occupy the middle of the county, collect specimens of its granite, and they will be found to offer a striking contrast to those of more fruitful districts; many other instances might be mentioned, but the geologist will have no difficulty in multiplying them. As a general rule it may be stated, that in order to obtain the

greatest fertility, the proportion of siliceous matter in a soil ought to be increased according to the quantity of rain that falls, or rather, perhaps, to the frequency of its recurrence; for it is evident, that one of the principal effects of this element, is to diminish in the soil its capacity for moisture; we accordingly find, that in the rainy climate of Turin, the most prolific soil has from 77 to 80 per cent. of siliceous, and from 9 to 14 of calcareous earth; whereas in the neighbourhood of Paris, where there is much less rain, the silex bears only the proportion of from 26 to 50 per cent. in the most fertile districts.

“Let the agriculturist of Cornwall, then, if there be any who repine at the moisture of their climate, hail with gladness those golden showers that fill their granaries with corn, and clothe their pastures with perpetual verdure.

"We cannot contemplate this circumstance, without discovering the agency of that intelligence which Nature so constantly displays in connecting the wants and necessities of the different parts of creation with the power and means of supplying them; thus, in primitive countries, like Cornwall, the soil necessarily requires moisture, and we perceive that the cause which occasions, at the same time supplies, this want; for the rocks elevated above the surface solicit a tribute from every passing cloud, whilst in alluvial and flat districts, where the soil is rich, deep, and retentive of moisture, the clouds float undisturbed over the plains, and the country frequently enjoys that long and uninterrupted series of dry weather which is so congenial and necessary to its fertility. Linnæus observes, that the plants which chiefly grow upon the summits of mountains are rarely found in any other situation, except