LIMING. 113"> 



obtain only what is true, and useful it would be necessary for him 

 first to understand the subject better than most of those whose 

 opinions he was studying. Indeed it was not possible for them to 

 be correct, when treating (as most writers do) of lime as one kind 

 of manure, and every different form of the carbonate of lime as so 

 many others. Only one distinction of this kind (as to mode of 

 operation and effects) should be made, and never lost sight of 

 and that is one of substance, still more than of name. Pure or 

 quick-lime, and carbonate of lime, are manures entirely different in 

 their powers and effects. But it should be remembered that the 

 substance that was pure lime when just burned, often becomes 

 carbonate of lime before it is used (by absorbing carbonic acid 

 from the atmosphere) ; still more frequently before a crop is 

 planted ; and probably always before the first crop ripens. Thus, 

 it should be borne in mind that the manure spoken of as lime is 

 often at first, and always at a later period, neither more nor less 

 than calcareous earth ; that lime, which at different periods is two 

 distinct kinds of manure, is considered in agricultural treatises as 

 only one ; and to calcareous earth are given as many different 

 names, all considered to have different values and effects, as there 

 are different forms and mixtures of the substance presented by 

 nature. 1835.] , 



But, however incorrect and inconvenient the term marl may be, 

 custom has too strongly fixed its application for any proposed 

 change to be adopted. Therefore, I must submit to use the word 

 marl to mean beds of fossil shells, notwithstanding my protest 

 against the property of its being so applied.* 



[* The geological character of this tide-water region renders impossible 

 the existence of true marl beds, which can only be sought for with hope, 

 if anywhere in Virginia, in the valleys of our mountain lime-stone 

 region where it would be as much in vain to seek for the fossil shells, so 

 abundant elsewhere. The latter deposit is the product of the ancient 

 ocean (during the tertiary formations), of which the bottom, with its beds 

 of shells, has been subsequently "up-heaved" to the position of dry land. 

 True marl, when found in considerable quantity, is usually, if not always, a 

 fresh-water formation ; being produced from the earth torn up and borne 

 along by rapid rivers and mountain streams, flowing over a chalky or 

 other highly calcareous country. By such suspension and intermingling, 

 the heavier sand is first dropped, and the still floating calcareous and 

 aluminous earths mix and then combine chemically in suitable proportions ; 

 and when the suspending water becomes nearly still, by reaching a lake 

 or estuary, the lightest earthy matter is deposited and forms marl. This 

 natural process continues until the receptacle is filled, and the deposit is 

 raised above the water. However much it may appear like fine clay in 

 some respects, true marl is very different in others. It is not in the least 

 plastic. If laid in water after drying, it speedily crumbles to small frag- 

 ments, showing a laminated structure, the result of the manner of its de- 

 position. Some olays, however, destitute of lime, exhibit this mechanical 



10* 



