110 A PRACTICAL TREATISE 



or stone ; for it contains both stimulant and fertilizing" proper- 

 ties which do not belong to the former, and from its effects 

 upon the soil it has been classed among animal manures, 

 tiiough it more properly resembles a compost formed of earth 

 and lime, with animal and vegetable substances, for whicii 

 reason it is justly considered preferable to the otJiers. It 

 exists at the bottom of most lakes; and under bogs and morasses, 

 or otlicr pieces of stagnant water which have been drained, 

 and might, no doubt, be found in every place where water has 

 originally rested : though, as it is usually under other layers 

 of earth or peat, its depth below the surface is often too great 

 to admit of its being searched for with advantage. Every 

 farmer should, therefore, carefully examine the sides and bot- 

 toms of his ditches and ponds, for, by doing so, he may often 

 find appearances of marl in places where it was not suspected, 

 and large beds of the most valuable sort have been in that 

 manner discovered, which might have remained unnoticed for 

 years. 



It is chiefly composed of those myriads of small shell-fish 

 which, with other fry and insects, usually procreate wherever 

 there are pools of water, and the remains of which have, in tlie 

 course of past ages, been deposited along with sand and decayed 

 vegetables, or other matter swept from eminences, or by the 

 decomposition of aquatic plants. This process of alluvion has, 

 in the lapse of time, produced those masses of shell-marl w hich 

 display the most striking effects when employed as manure ; 

 for the shells, when decomposed, are converted into lime of 

 such purity, that some moss-marl, examined by Dr. Coventry, 

 was found to contain 84 per cent, of pure chalk — which is 

 more than is generally possessed by the purest lime — and the 

 mould formed of the other substances must be very rich.* It 



* By other experiments made by Sir G. Mackenzie, it appeared that some 

 shell-marl was composed of 



Lime 41 25 



Carbonic acid 32 



Silex 14 



Aritil 4 y in 100 parts, (a) 



Oxide of iron .... 2 5 i 



Inflammable matter ... 2 



Loss 4 70 J 



(a) [The green sand of New Jersey is remarkable for its fertilizinsr pro- 

 perties. It goes under the name of marl; but it is differently constituted 

 from the marl spoken of in this work. Its power depends upon its plms- 

 phates. Its etTects in reclaimin-!; worn-out sandj- lands arc well known in 

 New Jersey, where its value is appreciated. In fact, it is sometimes too 

 much, appreciated; beuic relied upon to the exi hision of other manures, and 

 applied to all sorts of land, and for all kinds of crops.] 



