16 5 of alumina. These, in the vicinity of the dolerite, have become saturated with protoxyd bases, including the small portions of magnesia and of oxvd of iron which the limestone contains. This process evidently involves a decomposition of the carbonate. of lime, and the expulsion of the ca bonic acid. It is worthy of remark that while the unaltered limestone contains a little carbonate of magnesia, the rock from which III was obtained yielded to dilute nitric acid not a trace of magnesia. II marks an intermediate stage in the process, and shows moreover that the alkalies are still retained in combination with the alumonius silicate. These granular silicates, which have been formed by local metamorphism, might, under favorable circumstances, have crystallized in the forms of feldspar, scapolite, garnet, pyroxene, or some other of the silicious minerals which so often occur in metamorpic limestones. The agent in producing these silicates of protoxyds at the expense of the carbonates of the limestone, was probably a portion of alkaline salt, either derived from the feldspathic matter of the limestone, or possibly infiltrated from the contiguous feldspathic rock; whose elevated temperature prod..ced the reaction which has resulted in thus altering this limestone.

Similar examples of local alteration are m t with in several other places near to the intrusive rocks of the Montreal group. The schists of the Utica formation in contact with a dyke of intrusive rock at Point St. Charles, and also near a mass of trachyte on a small island opposite the city of Montreal, occasionally exhibit small crystals of pyroxene, and in some cases prisms of hornblende. Among similarly altered shales at Rougemont are beds which consist of a highly ferriferous crystalline dolomite intermingled with dark-green cleavable hornblende, which forms thin layers, or in other cases encloses small rounded masses of the dolomite. (See for a description and analyses of this rock the Geology of Canada, page 634.)

At Montarville the shales of the Hudson River formation are altered in the vicinity of the dolerite which forms the mass of the mountain. Some portions of the strata are very fine-grained, re Idish-brown, and have an earthy sub-conchoidal fracture, with occasional cleavage joints. The hardness of this rock is not great, and it is apparently a kind of argillite; but between two beds of it is one of a harder coarse-grained rock, greenish-gray in color, and mottled with a lighter hue. This appears to be feldspathic in

composition, and is penetrated in various directions by numerous slender prisms of black cleavable pyroxene, sometimes half an inch in length. The layers of sedimentation are distinctly marked in this bed, as well as in the finer-grained strata which enclose it; and the whole affords an interesting example of the different effects of the sun agency upon beds of unlike composition; although it would be impossible without comparative chemical analyses to determine whether the silicite which has here crystallized in the form of pyroxene existed in the unaltered sediment, or whether, as in the case of the uncrystallized silicate from the altered limestone at Montreal, it has been generated under the influence of the intrusive rock. In by far the greater number of cases, the only apparent effect of the igneous rocks in the region under description upon the palæ zoic limestones and shales, has been a very local induration. The appearance of crystals in these circumstances is a comparatively rare occurence, and seems to depend upon conditions which are exceptional, showing, as I have elsewhere remarked, that heat and moisture are not the only condition of metamorphism. (Silliman's Journal [2], xxxvi, 219.)

With these few examples of local metamorphism I conclude the present paper; proposing however to give in a subsequent one the results of some investigations of certain indigenous crystalline rocks. Montreal, March 15, 1864.

CHEMISTRY OF MANURES.*

CINEREAL CONSTITUENTS OF PLANTS.-It is not however exclusively by carbon, nitrogen, and the elements of water that

* Continued from page 124.

†This term cinereal, from cineres, ashes, may prove convenient to indicate, without periphrasis, the ash-constituents of plants in contradistinction from their volatile elements. Some writers fall into the error of employing the epithet "mineral" to denote the ash-ingredients; an error in nomenclature probably arising from some con used impression that, because of its earthy derivation, the ash of plants is more mineral in character than the volatile or gaseous elements which air supplies and fire dissipates. The illustrious author of the min ral-theory seems, in some of his earlier writings, himself to have countenanced this error. Nevertheless, its simple indication suffices for its refutation. Carbon and

plants are nourished; nor is it solely in quest of food, such as the leaves also can assimilate from the air, that the roots spread forth their manifold ramifications amidst the earth.

Liebeg first set forth, in all their peculiar interest and importance, the fixed ingredients of plants; that is the compounds which appear as ash, when the volatilizable air-derived elements of plants are burned off. These ash-ingredients constitute, as he explained, the special (though not the sole) food of the roots; and they are the only kind of nutriment which has its primary and exclusive source in the soil.

These essential ash-ingredients, so far as we yet know them, are the two fixed alkalies, potash and soda; two earthy bases, lime and magnesia; one heavy metallic base, oxide of iron; three acids, phosphoric, silicic, and sulphuric; and lastly, chlorine, which, though a gas, is always taken up by plants in fixed combinations (as for example in common salt), so as to remain in the ash or incineration.

Small as are the proportions of these fixed ingredients assimilated by plants during their growth, they are yet as necessary to the plant's development as the carbon and water which make up its main bulk. So again, as between the fixed ingredients themselves, although some of them are needed in larger, and some in smaller proportions, each species of plant having in this respect, its special requirements; although, for example, one ingredient may form more than one half the total ash of a given plant, and another less than a tenth part thereof; yet are they all equally essential to its development, which languishes as much for want of the minutest as of the bulkiest cinereal supply, Soils wholly deficient in any one of the ash ingredients of a particular plant, cannot produce that plant, howsoever abundantly every other of its elements, volatile and fixed, may be supplied. Partial deficiency of either of the normal ingredients of plant-food, whether fixed or volatile, involves a proportionately scanty crop; and no heaping of other

carbonic acid, nitrogen, ammonia, and nitric acid, oxygen, hydrogen, and water, all appertain to the mineral kingdom, in every sense as fully as silica, potash, the phosphates, &c. The epithet "mineral" applies therefore equally to all the elements, both volatile and fixed, of plant-food; it is for the separate designation of the fixed or ash constituents, that the epithet cinereal is proposed. In this sense (to test its convenience) it will be employed in the remainder of this section.

manures on the soil can have the slightest effect, so long as the one ingredient, wholly or partly deficient, remains unsupplied.

Nor does the mere presence of the cinereal plant-food in the soil suffice it must be availably present. That is, besides any portion, however large, of cinereal element, that may be held in mechanical isolation within the substance of the stones or clods, beyond the reach of the roots; or that may be locked up in chemical combination, too refractory for the solvent agencies present to subdue; besides any isolated or locked-up portion which may, in truth, be regarded as absent for all immediate purposes of nutrition; there must be a sufficiency of ash-constituents, held lightly, either by the surface-action of the moist and porous earth, or (according to another view) by the chemical attraction of the aluminous silicates, in such manner as to be, both physically and chemically, accessible to the roots. No doubt the locked-up materials of one season, may, and do become, in due course of tillage and fallowing, the accessible food of the next; and, indeed, it is to such gradually-decomposing reserves that the prolonged fertility of certain soils, worked by tillage and fallowing only, without manure, is due. But for all immediate purposes, a soil is exhausted, when, rich as it may be in the conditions of future fertility, it lacks an adequate present supply of the ash-constituents of plants, in free accessible diffusion.

HIGH FARMING: HOW FAR JUSTIFIABLE: AT WHAT POINT EXHAUSTIVE.—And here it becomes opportune to resume the question of high farming, which in a previous page was reserved for subsequent elucidation.

High farming, as already pointed out, is justifiable in so far as it serves to concentrate, within limits adapted to the assimilative powers and circumstances of annual and biennial plants, the foodsupplies diffused by nature over a much wider expanse of time and space, to suit vegetation of perennial growth. But it is of the deepest importance to observe, that the more abundant crops, and apparently increased fertility usually induced by high farming, are in too many cases but the premonitory symtoms of an accelerated process of exhaustion. The semblance of prosperous husbandry thus created is as factitious as the spendthrift's ruinous magnificence maintained by squandering his capital; and "high farming," even when coupled with "high manuring," and the keeping of many cattle for their dung, is often, for the unwary husbandman, only a flowery road to destruction.

For it is to be remembered that a soil may, by the excessive use of lime, common salt, nitrates, and other solvent or disintegrant manures, as also by diligent ploughing, scarifying, crushing, and other processes of mechanical comminution, be made to yield its reserves in accessible form, at an unduly accelerated rate. The same result may ensue, if the volatile forms of plant-food, which nature supplies only in moderate annual proportion, be added in pr fusion to the soil, without due care to conjoin therewith proportionate supplies of ash-constituents, or cinereal food.

ROTATION OF CROPS OFTEN EXHAUSTIVE.-Even the vaunted system of rotation-i. e., the growth of fodder-crops alternately with cereals, these latter receiving as manure the dung of the cattle fed on the former-is but too often so carried on as to be in truth a spoliatory operation; a sort of artifice, serving only to disguise and retard the period of final exhaustion; which so far from averting, it does but make more profound. For the powerful, deeply-penetrating roots of the fodder-crops extract from the subsoil its ash-constituents; which, after passing through the bodies of the cattle, are deposited in their dung on the surface, thence to sink into the upper layers of the soil, and so to find their way to the fibres of the young, slender-rooted cereal plants; in whose grain they are finally exported from the farm.

LOIS-WEEDON SYSTEM; ITS SPOLIATORY CHARACTER. The so-called Lois- Weedon system of cultivation is open to similar obje tion. This system, as is well known, consists in the glowing, year after year, upon soil which is never manured, of cornplants thinly sown in rows, separated by wide intervals; the intervals being each year stirred and fallowed, to become the next year's growing spaces; and so on in annual alternation. This system of husbandry, which may be regarded as an extreme exempincation of Jethro Tull's doctrine, is stated to have elicited from the melds in which it is pursued, a series of full grain-crops for many years in succession. This result is in the highest degree probable. And this apparent prosperity may be kept up for a series of years, longer or shorter for each soil, as this may happen to have been originally more or less richly endowed by nature with cinereal plant-food. But the end of this method also is exnaustion, -inevitable foredoomed exhaustion, -exuaustion of which each prosperous" crop is but an advancing stage, and whose rate the chemist measures, with stern precision, in the annually lessening