entering to any notable extent into the actual composition of plants, yet iron is one of the most important elements of soils in aiding plants to grow. It shares this function with organic matter. They are both stimulants, increasing the nutrition by the supply of oxygen which they yield to other proximate principles of vegetation. The iron of a soil is generally reported in an analysis as existing in the state of peroxide; but, strictly speaking, no. soil contains iron in state of peroxide alone. Some of it is in the form of protoxide, brought to this condition by organic matter, which has robbed the peroxide of some of its oxygen. In this double state it exists in greensand. The organic matter of a soil, by contact with oxide of iron becoming oxidized, is changed into vegetable acids which are soluble, and unite with the lime and magnesia to form soluble salts of those earths, which then enter the rootlets of the plant and aid in forming tissue in the sap. Perhaps the fertility of basaltic soils is as much due to their oxides of iron as to the lime which they contain.

This reaction of iron oxides and organic matter upon each other occurs only in the presence of moisture and sunlight, (heat;) and moisture itself, with heat, is at times a fertile cause of oxidation, and of the nutrition of plants. Away from the influence of these forces of nature the action of protoxide of iron is only injurious to vegetation. Under solar influence and contact of protoxide of iron, water itself is decomposed, its oxygen appropriated by the iron to peroxidize it, and the hydrogen liberated. The latter, coming into contact with the nitrogen of the air, forms ammonia, which is seized by carbonic and other organic acids, rendered soluble in water, and fit to enter the plant. Thus, iron is the medium between the water, the organic matter, and the atmosphere.

These remarks are made to illustrate the action of greensand marls upon vegetation as far as their iron element is concerned. In these marls it exists chiefly in the state of peroxide, which, upon mixture with vegetable matters, is reduced to protoxide by contact with the moist humus; then, being restored to the condition of peroxide by contact with moisture, the consequent liberation of hydrogen forms ammonia secondarily. Íron thus aids in forming soluble organic matter, as organic acids, and also ammonia, two important principles of fertility. We should, therefore, err if we estimated the value of a greensand by taking into account only its lime, its potash, or its phosphoric acid. We should consider the oxide of iron as a valuable constituent in promoting fertility. The presence of potash in these marls gives them their distinctive character as fertilizers, and adds one of the most important elements necessary for plants. The large amount of potash found in glauconite renders it at once the cheapest source for agricultural use from which this mineral element can be supplied. The action of potash is twofold: first, upon the insoluble organic matter of a soil, bringing it into a sol uble form; and, secondly, supplying to certain food plants the special alkaline food which they require. By the constant action of alkalies, (and of this class potash is the most efficient,) the insoluble organic matter, humus is converted into humic acid, and carbonic acid is also. produced. Both of these acids ultimately unite with the potash and form carbonates of that base, which salts, when formed, enter the rootlets of the plants in a limited degree, remain for a short period in the vegetable organization, and are then ejected-perhaps not wholly. Under this influence the woody tissues of plants are formed In the development of leaf and tuber potash seems essential. It is chiefly aggregated in the leaves of most plants, as it is in the muscular

juices of animals, forming not less than twenty and sometimes more than fifty per cent. of the leaf weight-the latter amount being found in the roots and tubers. The straw and chaff of cereals also contain it in variable proportion. Perhaps nowhere is the selecting power of plants for special mineral salts better shown than in the distribution of potassa. Dr. Anderson illustrates this by the case of the poppy, which contains only twelve per cent. of this alkali in its seed, while the leaves yield upward of thirty-seven per cent.

Sufficient has already been written concerning the value of phosphoric acid and phosphate of lime to render any statement unnecessary here. All cretaceous marls contain phosphoric acid, whether combined with iron or lime; and phosphate of lime is, perhaps, more valuable than lime as a fertilizing agent. The form in which potassa exists in these marls is as a silicate, and it is slowly decomposed under mere atmospheric exposure. On soils which contain lime or much humus, the decomposition proceeds at a more rapid rate, owing to the evolution of carbonic acid; and in this way this alkali is slowly evolved for the benefit of vegetation. The long-continued beneficial action of greensand on grounds may in part be explained by the gradual nature of this decomposition. In New Jersey, along the line of the Raritan and Delaware Bay railroad, where it is sold at eight cents a bushel, it is applied at the rate of one hundred bushels per acre; and on these light soils produces a better effect than the usual dressing with stable manure, especially for small fruits and market-garden vegetables. In Delaware, from three hundred to five hundred bushels have been applied per acre for wheat, oats, and other cereals, with sometimes a fourfold return. A decided benefit, but not to the same extent, is experienced on grass. Generally, it may be said that land has increased by its use from fifty to one hundred per cent. in value. The value of marling south of New Jersey is the combined value of the carbonate and the phosphate of lime, and of the potassa. When the marls are more calcareous, they become amendments to the soil rather than fertilizers to the crops, and much larger dressings are therefore necessary; while, at the same time, more discrimination is required as to the land which will be mainly benefited by the application. The lime being in predominant quantity in the greensand marls south of Delaware, the action is chiefly upon the organic matter of the soil, combining with it and rendering it more soluble. Hence, to poor and light soils it would be unnecessary to apply heavy dressings; for these, fifty to eighty bushels per acre might be sufficient. On stiff, clayey soils, the texture of which may be lightened advantageously, from one hundred to three hundred bushels per acre may be applied. In these clay soils there is generally more insoluble organic matter to be acted upon, and in such cases so large a quantity as five hundred bushels per acre acts beneficially. In general terms, then, it may be stated that the calcareous greensand marls act more effectively in proportion as there is organic matter present, and in proportion as the clay is a heavy one.

It is not easy to determine exactly the value of a compound manure like this. The question is a commercial one, and would not properly be discussed here were not the value in a great degree dependent upon the chemical analysis. Were the fertilizer composed of but one ingredient, it would be easy to determine its value by ascertaining the market price of the pure and commercial article, and then determining how much of such ingredient existed in the manure. Thus, if phosphoric acid in a soluble state is worth commercially fifteen cents per pound, and the

fertilizer contains one hundred pounds in a ton, it is evidently worth fifteen dollars per ton when delivered.

When a manure has a complex constitution, the real value becomes a difficult problem to state exactly, for the agricultural and the commercial value do not always agree. The former is fixed and invariable, dependent on the necessities of the plant and the soil; the latter is liable to fluctuation from the unsteadiness of the supply and demand. The following estimate is approximately correct. The value of phosphoric acid in the soluble form may be set down at fifteen or sixteen cents per pound; phosphoric acid in insoluble form, six cents per pound; potash in the soluble form, seven cents per pound; potash in the insoluble form, two cents per pound; sulphuric acid, one cent per pound; carbonate of lime, half a cent per pound. If we calculate the value of one of the inferior greensand marls of Maryland, as No. 3, from Prince George's County, we obtain:

320 pounds carbonate of lime, at cent..

6 pounds soda salts, at 1 cent..

2 pounds phosphoric acid, insoluble, at 6 cents.

1

pounds potash, soluble, at 7 cents..

20 pounds sulphuric acid, at 1 cent.

$1 60

06

12

11

26

2 15

This estimate is somewhat below the real value of the compound, since it estimates each article singly, and takes no account of the effect of the different ingredients of the mass upon one another in rendering them more readily soluble, more stimulating to and more fit for appropriation by the plant. The general method of calculating values, however, may be of interest to many who desire to know how estimates should be made.

What we have just stated--that the value of a compound manure is greater than the sum of the values of its separate constituents-needs some remark; otherwise, and with justice, the farmer might say: "Why should I dig and haul so bulky a material as this marl, containing as it does not more than five positively useful ingredients, amounting to ten per cent. of the whole weight, when I can buy these several salts from the wholesale druggist, and then dilute them afterward on the ground? Would it not be actually cheaper to buy the chemicals and make my own compost, rather than to take the bulky form in which nature supplies them?" The answer to these questions lies in the following considerations: Admitting that both the artificial salts and the natural marl have an equal manurial value and action, still the farmer should remember that he is often richer in cattle and human labor than in ready money; that in idle seasons he can haul and spread his native marl, (if it is a month or two sooner than it is actually needed, it suffers but little from exposure,) while, as regards the purchased salts, they must be bought only when required, as they waste and lose by exposure to the air and moisture. They can be applied only at a certain period for the benefit of the growing crop, because they readily dissolve in water. They act readily on the crop, and are effective during the particular season in which they are applied; but their action, while immediate, is also transitory. It is felt less the next year, very much less the following year, and subsequently cannot be recognized except, perhaps, by a diminished productiveness of soil. On the other hand, in the case of natural marls, the elements are but sparingly soluble, and consequently

given out only by little at a time, as the plant needs and has ability to appropriate. Hence their action, while slow, is of a permanent character, and can be ascertained after many years. In New Jersey one of the first applications of greensand, over sixty years ago, so enriched the field that it was recognizable as improved thirty years after the application; and in North Carolina the alluvial lands which have been manured with these marls have retained their superiority over unmarled lands for over fifty years without a second dressing. When this increased and permanent fertility has been experienced, it is not wonderful that the natural should be preferred to the artificial compounds, or that over one million bushels of greensand marl should have been dug and sold in New Jersey in 1868.

NATIVE PHOSPHATIC MANURES.

During the year, samples of mineral from the newly discovered phosphatic beds of Charleston, South Carolina, were forwarded for analysis. These beds have received great attention lately, owing to their containing a large amount of phosphate of lime; and much has been communicated to the public concerning them, by Drs. Pratt and Holmes, and Professor C. U. Shepard, jr., M. D., of Charleston. Their geological position as strata had long been known and described, but it has been only within the past few years that their extreme richness in phosphate of lime at once classed them as one of the most valuable mineral beds of South Carolina.

The strata containing phosphate of lime range in position, in South Carolina, from the early miocene to the middle bed of the post pliocene formation. It was during the early tertiary period that the greater portion of the shore land of the Carolinas, and south by Mobile River to the western limits of Louisiana, was formed by deposition and subsequent extensive, slow, and uniform elevation. The Claiborne marls and shell sands of Alabaina are the lowest beds of this series, with the more solid buhr-stone and the white limestone marls of the Santee River. Above these, in the same group, occur the gray marls of the Ashley and the Cooper Rivers, abounding in rhizopods. These are miocene beds, and upon them lie, unconformably, the post pliocene sands and marls, one of which embraces the material now so much sought after for its agricultural value.

All of these strata contain phosphate of lime in marked quantity. The marl beds of Charleston are of wide extent, embracing, according to Dr. Tuomey, an area of seventy-five miles by sixty, from the Santee River on the east to the Ashepoo on the west, and lying between the Atlantic Ocean on the south and east and the buhr-stone formation of the eocene beds on the north. They are beds of white limestone marl and greensand, dipping gently to the south, and underlying the newer beds of marl of the Ashley and Cooper Rivers, the former of which constitutes the uppermost stratum of the eocene. The thickness of the Santee beds is between six hundred and seven hundred feet, and has been recognized as underlying the whole neighborhood of Charleston. Dr. Smith and Professor Shepard found what was deemed an unusual amount of phosphate of lime, ranging from two to nine per cent. of that mineral. This amount, while constituting a rich soil, did not justify its use or transportation as a marl, the value of which is to be estimated by the amount of lime phosphate it contains. The quantity of carbonate of lime is very great, varying from fifty to eighty per cent., and the value had hitherto been estimated according to the amount of this ingredient.

The fish-beds of the Ashley River yielded to Professor Shepard the fol lowing constituents:

No. 1, from Mr. J. P. Clements, west of Ashley River; No. 2, from Rev. Dr. Hankels, bank of Ashley River; No. 3, from Drayton Hall, bank of Ashley River; No. 4, from Wilmington, North Carolina.

The first three analyses give the average composition of this stratum about Charleston. No. 4 gives the constitution further north, showing that it becomes more purely calcareous as it passes northward, until it finally thins out and disappears before it reaches New Jersey.

Above this bed of calcareous marl is a layer of blue sand, in which are found hard masses of grayish or bluish-white rock, which break readily into fragments, and have been called nodules. These constitute the material now so much sought after, and are described by Dr. Tuomey, in his survey of South Carolina, as scattered over the surface, so as, in some places, to offer obstruction to the cultivation of the land, and therefore have been gathered in heaps from the land of the plantations near the Ashley River, in order to render cultivation possible.

Professor Shepard, jr., in an article in the Massachusetts Ploughman on these phosphatic beds, describes their appearances as follows: "The chief beds were discovered on the Ashley River, extending from about seven miles above Charleston up the river for ten to fifteen miles. The land is not level but rolls in low bluffs, generally twenty to forty feet high, at right angles to the course of the river. Between these bluffs there are swamp lands, most of which have canals through them, and were once thoroughly drained for the culture of cotton. In these low lands the rich top soil is about four to six inches in depth; there follows a light sandy stratum sometimes eighteen inches thick, generally less; and, underneath, the stratum of nodular phosphates, packed close together with hardly any soil between them." Professor Holmes had, as far back as 1844, described the occurrence of a conglomerate layer, consisting of nodules imbedded in a blue sandy clay, about twelve inches thick, overlying the marl beds the composition of which has just been given. They require the use of the pick to remove them, and are locally called marl-stones. The remains of marine and of terrestrial animals are found in this bed, and casts of fossils common to the marl bed below, (Holmes.) It is remarkable that these nodules and fossil remains were looked upon as pseudomorphs in which the carbonate of lime has disappeared, to be replaced by silica; the phosphate of lime having escaped recognition until its real composition was declared by Dr. N. A. Pratt, from examination of several of the nodules in August, 1867, which revealed the fact of a large percentage of phosphate of lime, instead of silica, in them. According to a statement made in a pamphlet entitled "Ashley River Phosphates," and printed in Philadelphia at the close of 1868, Dr. P. found in these nodules as much as 34, 55, and 66 per cent. respectively; in fact they were true bone phosphates, in some samples of which the amount of phosphate exceeds that found in bones of living mammals. This discovery led to the formation of a company, residing in Philadelphia, to raise and export the material. The works