108 FOSSIL SHELLS AND MARL. 



reduced nearly to a coarse powder. The earth which fills their 

 vacancies, and serves to make the whole a compact mass, in most 

 cases is principally silicious sand, and usually contains no putres- 

 cent or valuable matter, other than the calcareous.* The same 

 effects, in the main, might be expected from calcareous earth in 

 any other form, whether chalk, lime-stone gravel, wood ashes, or 

 lime though the two last have other qualities besides the calca- 

 reous. During the short time that lime can remain quick or caustic, 

 after being applied as manure, it exerts (as before stated) a solvent 

 power, sometimes beneficial and at others hurtful, which has no 

 connexion with its subsequent and permanent action as calcareous 

 earth. 



These natural deposits of fossil shells are commonly, but very 

 improperly, called marl. This misapplied term is particularly ob- 

 jectionable, because it induces erroneous views of this manure. 

 Other earthy manures have long been used in Europe under the 

 name of marl, and numerous publications have described their 

 general effects, and recommended their use. When the same name 

 is given here to a different manure, many persons will consider 

 both operations as similar, and perhaps may refer to English 

 authorities for the purpose of testing the truth of my opinions, 

 and the results of my practice. But no two operations called by 

 the same name can well differ more. The process which it is my 

 object to recommend, is calxing, or simply the application of calca- 

 reous earth in any form whatever, to soils wanting that ingredient, 

 and generally being quite destitute of it ; and the propriety of the 

 application depends entirely on the knowing that the manure con- 

 tains calcareous earth, and what proportion, and that the soil con- 

 tains none. In England, the most scientific agriculturists apply 

 the term marl correctly to a calcareous clay of peculiar texture. 

 But many authors, as well as the illiterate cultivators, have used 

 that name for any smooth soapy clay, which may or may not have 

 contained, so far as they knew, any proportion whatever of calca- 

 reous matter. Indeed, in most cases, they have seemed uncon- 

 scious of the presence as well as of the importance of that ingre- 

 dient, by their not alluding to it when attempting most carefully to 

 point out the distinguishing characters by which marl maybe known. 

 Still less have they inquired into the deficiency of calcareous earth 

 in soils proposed to be marled but applied any earth which either 

 science or ignorance may have called marl, to any soils within a 



[* From later observation I have formed the opinion that the colouring 

 matter of blue marls is vegetable extract, chemically combined with the 

 calcareous matter, of which opinion the grounds will be stated hereafter. 

 But still the amount of this vegetable admixture is too small to have much 

 appreciable effect as food for plants ; and, for all practical use, the general 

 position assumed above may yet be considered as altogether true. 1842.] 



