132 CALCAREOUS MANURES— APPENDIX. 



4. Walker's Dictionary (octavo edition) gives only the following defini- 

 tion — " Marl — a kind of clay much used for manure." 



5. A Practical Treatise on Husbandry, (2nd London edition 4to, 1762,) 

 which professes to be principally compiled from the writings of Duhamel, 

 Evelyn, Home, and Miller, supplies the following quotations : 



" But of all the manures for sandy soils, none is so good as marl. There are many 

 different kinds and colors of it, severally distinguished by many writers ; but their vir- 

 tue is the same ; they may be all used upon the same ground, without the smallest dif- 

 ference in their effect. The color is either red, brown, yellow, gray, or mixed. It is to 

 be known by its pure and uncompounded nature. There are many marks to distinguish 

 it by ; such as its breaking into litlle square bits ; its falling easily into pieces, by the 

 force of a blow, or upon being exposed to the sun and the frost ; its feeling fat and oily, 

 and shining when 'tis dry. But the inost unerring way to judge of marl, and know it from 

 any other substance, is to break a piece as big as a nutmeg, and when it is quite dry, 

 drop it into a glass of clear water, where, if it be right, it will dissolve and crumble, as it 

 were, to dust, in a little time, shooting up sparkles to the surface of the water." — p. 27. 



— Not the slightest hint is here of any calcareous ingredient being neces- 

 sary, or even serving in any nianncr to distinguish marl. But afterwards, 

 in another part of this work, when shell marl is slightly noticed, it is said : 



" This effervesces strongly with all acids, which is perhaps chiefly owing to the shells. 

 ITiere are very good mails which shoto nothing of this effervescence : and therefore the 

 author of the New System of Agriculture judged right in making its solution in water the 

 distinguishing mark." — p. 29. 



The last sentence declares, as clearly as any words could do, that, in 

 the opinion of the author, no calcareous ingredient is necessary, either to 

 constitute the character, or the value of marl. And though it may be ga- 

 thered from other parts of this work, that what is called marl generally 

 contains calcareous earth, yet no importance seems attached to that quality, 

 any more than to the particular color of the earth, or any other accidental 

 or immaterial appearance of some of the varieties described. 



The " shell marl" alluded to above, without explanation might be sup- 

 posed to be similar to our beds of fossil shells, which are called marl. The 

 two manures are very different in form, appearance, and value, though 

 agreeing in both being calcareous. The manure called shell marl by the 

 work last quoted from, is described there with sufficient precision, and more 

 fully in several parts of the Edinburgh Farmer's Magazine,* and in the Me- 

 moirs of the Philadelphia Agricultural Society.f It is still more unlike 

 marl, properly so called, than any of the substances described under that 

 name, in the foregoing quotations. This manure is almost a pure calca- 

 reous earth, being formed of the remains of small fresh-water shells de- 

 posited on what were once the bottoms of lakes, but which have since be- 

 come covered with bog or peat soil. If I may judge from our beds of mus- 

 cle shells, (to which this manure seems to bear most resemblance,) much 

 putrescent animal matter is combined with, and serves to give additional 

 value to these bodies of shells. This kind of manure is sold in Scotland 

 by the bushel, at such prices as show that it is very highly prized. It 

 seems to be found but in few situations, and though called a kind of marl, 

 is never meant when that term alone is used generally. 



A much older work than either of these referred to furnishes in part 

 the definitions and even the words used above. This is the '■Systema Ag- 

 riculturcE, the Mystery of Husbandry discovered, published in 1687; and the 

 author or compiler of that old work was probably indebted to others still 

 older for his description of marl. For new books on agriculture, more 



* See Farmer's Register, vol. i., p. 90. 

 t Vol. iii. p. 206. 



