244 



F A II M E R S ' R E G I S T IC R . 



[No. 4 



application of this marl has been found peculiarly 

 fidvanta^eous: and on all poor and thin sandy soils 

 there is this lijrther advantage in its iise — that, 

 li'om the large proportion of clay which it usually 

 contains, it adds to their bulk and firmness, and 

 thus has a tendency to bring them to that medium 

 state which is the most favorable to the purposes 

 of vegetation. It is more soft and unctuous than 

 clay; indeed, upon slightly cutting it, it becomes 

 so flexible, that it may be kneaded like dough, or 

 pasie, though, when the moisture evaporates, it 

 falls into pieces: it therefore blends easily with the 

 soil, and partaking more laigely of calcareous 

 matter, its effects, though slow, are in all the latter 

 cases more fertilizing. 



2. Sandy marl, which is far more frequent in 

 Ireland than in any part of England, and is com- 

 monly found in pits of limestone-g-ravel, whence 

 it is in that country usually called limestone-sand. 

 It is seldom clammy or unctuous, like the clay 

 marl, nor does it adhere to the tongue, but crum- 

 bles between the fingers, and feels gritty; when 

 exposed to the air and moisture it slowly chips 

 and moulders; and it partakes of some extraneous 

 mixtures. Its color is sometimes hke that of lead, 

 or brown. approaching to black, and at others blue. 

 As implied by its name, 4t contains an excess of 

 sand over that of clay; for, upon analyzing it, the 

 proportion of the former has, in most cases, been 

 found to be from 60^0 80 percent.; and it does 

 not effervesce with acids so quickly as the calca- 

 reous marls, It possesses but a small degree of 

 tenacity, and it has proved an excellent manure for 

 claj'ey soils, mellowing their stiffness, and render- 

 ing them easier to work. 



3. Slaty or stony marl, to which class, also, pro- 

 perly belongs that which is called rotten limestone, 

 is chiefly applied to heavy land. Its operation is 

 kIovv, but very lasting; land, forty years after it 

 has been laid on, having been found to bear a 

 closer and a better crop of grass than that which 

 had been recently applied. 



4. Shelly marl, which is evidently produced by 

 the remains of testaceous fish, which, dying in 

 their shells, become, in process of time, converted 

 into calcareous earth, and their bodies, when de- 

 composed, furnish a kind of mould composed of 

 animal substance, which is no doubt analogous to 

 the effect of dung. It is, therefore, highly ferti- 

 lizing when judiciously applied to soils of every 

 kind, which are either in themselves dry, or which 

 have been properly drained. 



Such are the most common denominations by 

 which marl is usually distinguished, though it is 

 susceptible of many subdivisions by those who af- 

 fect to treat the subject scientifically. It is, how- 

 ever; more fi-equentiy classed under the sole char- 

 acters of siliceous, argilaceous, or calcareous, ac- 

 cording as sand, clay, or lime predominates in its 

 composition; but, for all practical purposes, it may 

 be suflicient to divide it into earth-marl and shell- 

 vmrl. 



Earlh-marl. 



The former, though in substance, as we have 

 already seen, somefimes principally formed of 

 sand, is yet, m most cases, chiefly composed of 

 clay, and of the carbonate of lime, ultimately 

 combined, but mixed in very different proporlions, 

 by which its properties arc necessarily varied. It 



acts as manure physically, or substantial!)', through 

 the effect of the clay, in rendering soils tenacious; 

 and chemically, by ihe operation of lime, in the 

 manner which has been explained in treating of 

 that fossil. These two substances are so com- 

 pletely amalgamated, that it is not possible, either 

 by the eye, or even by a microscope, to distingush 

 the constituent particles of the one or of the other; 

 the fiict can, therefore, be only ascertained by 

 chemical analysis, and the means which nature 

 has employed in thpir combination is yet unknown; 

 lor although it might be supposed that mixtures 

 of clay and lime would produce the same eflect as 

 marl, yet they will not fall to powder in the same 

 manner when exposed to air; and it contains some 

 other fertilizing qualities with Ihe powers of which 

 we are unacquainted. Thus, in the improvement 

 of Chat Moss, in Lancashire, if a piece of marl 

 was suflered to lie a few months upon the ground, 

 it was found, on raising it up, that a considerable 

 quantity of the moss adhered to it; and if the in- 

 termediate substance was examined, it appeared 

 to be a mixture of marl and peat, formed into a 

 mucilaginous mass of a dark color, and as soft as 

 soap.* 



Although it is very generally thought that ex- 

 treme accuracy in philosophical experiments is use- 

 less in the practice of agriculture, yet it is particu- 

 larly necessary to ascertain the precise difference 

 between these modes of action; for, of course, 

 either one or the other prevails, according to the 

 greater or the less quantity of clay of which the 

 marl is composed. Thus, to produce the first 

 named, or jjhysical effect, a much larger amount 

 must belaid upon the land than when the second 

 is the object; for clay can only be advantageously 

 employed in that view upon soils that are too light; 

 and consequently the marl must be laid in pro- 

 portionate abundance, or it will not improve the 

 condition of the ground; whilst a clayey soil 

 would, on the contrary, lose some of its good qual- 

 ities by the addition of marl, after the effects of 

 the lime were exhausted. The intimate combi- 

 nation of these two substances in the composition 

 of marl aflbrds it, however, this advantage — that 

 it divides, and falls to powder, with greater ease 

 than can be effected by any artificial mixture, and 

 therefore unites more readily with the soil. 



On the other hand, if the calcareous matter in 

 the marl be combined with sand instead of clay, 

 or that there are, as in many instances, veins of' 

 calcareous sand intermixed, then it suits a clayey 

 soil. The proi)ortion in which these substances 

 are combined is, however, so different, that they 

 often vary in the same vein, and it is generally 

 found that the bottom partis more calcareous than 

 the top. From 15 to 40 per cent, is not unfre- 

 quently the portion of calcareous matter found in 

 clay; that of" a sandy nature generally contauis a 

 larger proportion.! 



* Communications to the Board of Agriculture, vol. 

 vli., art. xliv. See also Stevenson's edition of Dick- 

 son's Survey of Lancashire, chap. xii. sect. 3. 



t Argilaceous marl usually contains from 68 to 80 

 per cent, of clay, and from .32 to 20 per cent, of cal- 

 careous matter: but it has been found composed of 70 

 per cent, of calcareous, and 8 to 10 of sand, with clear 

 signs of some iron. 



Siliceous marl very often contains above 75 per 



