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MINERAL FERTILIZERS OF THE ATLANTIC
The economy and necessity of the use of mineral fertilizers have been so long admitted and are now so generally appreciated that it is deemed sufficient, in the limits of this article, to state the locality, extent, and nature of the wide-spread and liberal deposits of mineral manures in the Atlantic States, with some analyses, and such statistics as are attainable, showing their accessibility and cost.
Fertilization, in its widest sense, includes two processes : 1st, supplying the soil with materials intended to furnish plant food, either directly or by rendering available substances already present; 2d, the addition of matter for its physical effect merely; the former method is chemical, the latter mechanical, fertilization. Lime and greensand are examples, among mineral agents, of the first class; sand and clay of the second.
The elements supplied to the plant by mineral fertilizers are (omitting the least important, and those existing in the vegetable but in extremely minute quantities) lime, soda, potash, and acids of pliosphorus and sul. phur. Fertilizers of this class, then, generally speaking, will include all minerals capable of supplying these materials, either with or without chemical or mechanical preparation prior to admixture with the soil. Practically, however, the number of substances used is determined by the ingredients needed by the plants cultivated and lacking in soils, and the expense of obtaining them and reducing them to a form easily assimilable by the vegetable.
Lime constitutes the base of all the important fertilizers of this class in the United States, excepting the greensand marls, of which the New Jersey formation is the type, in which the percentage of lime is so small that it may practically be left out of consideration.
Limestone, or natural stratified carbonate of lime, in all its varieties, is available for agricultural purposes wherever it can be economically mined and prepared. This preparation consists essentially in the reduction of the stone to a finely comminuted state, which is usually accomplished by burning. In districts where fuel is scarce and water-power at hand, stamping or grinding may be found more economical, though the product will be slower in its action; and, lacking the causticity of burned lime, will not aid so effectually in the decomposition of organic matter.
Admixture of magnesia with lime is not now, as once, believed to be injurious to the fertilizing power of the latter. Dolomites and dolomitic limestones accordingly find a place among mineral manures; but, from their composition, are necessarily less efficient than the purer limestones.
Sulphate of lime, gypsum or plaster, has a well-established and high rank among fertilizing agents, furnishing to the soil sulphuric acid, in a readily assimilable form, as well as lime; and, though not widely disseminated, exists in large quantities, so as to be cheaply obtainable at most points.
Phosphate of lime is found in many natural forms. The shell beds, sands, and marls contain it; and one or two veins of almost pure apatite have been opened. The fossil excrement of marine animals, known as coprolites, is very rich in phosphate of linc; and, although not found in great mass in the United States, foris an important part of many of the richest marls of the south. By far the most important source of this material, however, is the recently discovered deposit of South Carolina. While lime may be considered the base of this fertilizer, un. doubtedly its most important ingredient is its phosphoric acid.
The term “marl” having so many and such different significations, dependent upon local usages, as well as the various classifications of scien. tific geologists, it is highly desirable that it should be limited to some specific fertilizing material or class of materials, rather than, as now, be made to include deposits as far apart in their chemical constitution and . value as in their period of formation. At least, when used, it should be so qualified as to indicate the mineral species to which the substance belongs.
The marls of the United States may be divided into argillaceous, glauconitic or greensand, and calcareous. Argillaceous marls are of comparatively little agricultural value, if we consider their chemica! constitution only, consisting mainly of clay and sand, with a trifling percentage of lime. There are circumstances, however, as before alluded to, in which they may become true and valuable fertilizers. Glauconitic marls include the greensands of New Jersey, Delaware, and Maryland, and a few localities further south. They are dependent, for their power of permanent beneficial action, upon the potash and phosphoric acid they contain. Full analyses of these deposits will be found in the report of the chemist.
Calcareous marls are the débris of countless successive generations of life, the remains of which may or may not be recognizable, according to the amount of pulverization and attrition they have undergone from the motion of the water in which they were deposited, and the subse. quent conditions to which they have been exposed. These deposits range in time from the cretaceous epoch of geologists to the present era, and are even now in process of formation both in marine and inland waters. They are found in greatest amount in the tertiary strata.
The foregoing account of the origin of marl applies with equal force to most of the limestones. Marls, however, are generally understood to be friable to a considerable extent, and this, together with the fact that many of the marls retain a sensible proportion of organic matter, constitutes a line of distinction between the two. This line is one, how. ever, often hard to draw; for, if it is true that even the hard and crystalline limestones are but the result of various forces, as heat and pres. sure, acting upon sedimentary strata containing organic remains, it is evident that there may be all grades of consolidation and homogeneity according to circumstances.
The physical character of calcareous marls varies with the class of animals, remains of which form their active ingredient, and the state of preservation of the latter; and their agricultural value varies with the proportion of inert matter they contain, and which frequently forms a matrix for the shells and other organic formations.
The deposits known as pond marl, or sometimes as shell marl, found in our lakes and ponds, or upon their former sites, and often under peat, explain, by their formation, which may be watched in all stages, the mode of origin of the greater part of the calcareous group. Water containing carbonic acid is, under pressure, a solvent of carbonate of lime, from which the microscopic testaceous animals inhabiting such water, by absorption and secretion, form their shells; and, dying, these are deposited, either to accumulate in vast masses, or, if the water is not
suficiently charged with lime, to be redissolved, reabsorbed, and to sup. ply new generations with covering.
Any excess of carbonate of lime in the earth is absorbed in the passage of the water through it; and thus deposits of this kind form chiefly in limestone regions.
In some localities a process similar to the foregoing has caused the formation of large beds of silicious marl, so called. Various species of phytozoa-organisms occupying the border between the animal and the vegetable kingdom, and in spite of many attempts to locate and classify them, not yet definitely assigned to either possess a shell or skeleton of silica. These accumulate, as in the case of the testacea, and like the calcareous pond marls are both fossil and recent. The beds underlying Richmond, Virginia, are of the former character.
Silicious marl, being a fertilizer only in the sense that fine sand is, namely, a physical amendment, will not be further noticed ; as it is now believed that all soils contain sufficient silica to supply the wants of plant life, and only require assistance in rendering it soluble.
Pond mari, from its friability, minute division, and superficial location, is, in districts where it can be bad, the cheapest and best of the purely calcareous manures. It may be applied as extracted or in a calcined condition. In some localities large amounts of this marl are manufactured into lime.
The recent calcareous tufa, travertin or calcareous sinter, formed by the precipitation of carbonate of lime direct from its solution in water when exposed to the air, is often called marl. It is, however, a true and pure limestone; and, physically much resembling the pond marl, is for the same reasons a cheap and ready fertilizer.
Few States having, as yet, been throughly surveyed with reference to their agricultural and their geological character and economical resources, statistics are necessarily incomplete, and much fuller for some regions than for others of perhaps equal importance. The object of this article, however, being as inuch to point out deficiencies as to present the results of investigations already undertaken, such information as is accessible will be presented, in the hope that those interested may be induced to communicate more complete and recent information.
If the recent discoveries on the southeastern coast may be taken as an indication of what is to follow, the field of research is indeed an inviting one.
The older calcareous formations of the Atlantic States constitute a belt of considerable breadth, coinciding nearly with the great eastern mountain chain of the continent, and having numerous offshoots and local outcrops, at greater or less distances from the main range. (See inap.) In the eastern States the limestones belong to the so-called Azoic, and to the Lower and the Upper Silurian formations; in other words, the earlier geological agesThe limestone of the Upper Silurian enters Maine from New Brunswick on the northeast; while the same together with the Lower Silurian (Trenton) appears in the moutains of Vermont. Extending along the east line of New York, and approaching somewhat near the coast in northern New Jerser, the limestone belt described passes through Western Virginia, North Carolina, and northern Georgia to its southern limit in northern Alabama.
The newer calcareous rocks and deposits belong either to the Carbon. iferous, the Cretaceous, or the Tertiary formation. The Carboniferous limestone appears in Pennsylvania, and, lying west of and parallel to the Silurian, is traceable to the same distance southwest, occasionally being found in or cast of the tract occupied by the older rocks.