ELEMENTS OF AGRICULTURE. 
LESSON V. 
MARL AS AN AMELIORATOR. 
29. We have seen (No. 42, second part), that marl is 
a compound of carbonate of lime mixed with clay, silica, 
shells, and other inorganic substances, in various propor¬ 
tions. The quantity of calcareous principles that a marl 
contains has a direct influence upon its use as an amelio¬ 
rator, and for this reason it has been thought useful to dis¬ 
tinguish several kinds of marl, that each suit soils of a 
different nature. 
30. The principal kinds of marl are : 1. The calcareous; 
those containing the most carbonate of lime, and which 
are consequently the richest. 2. Marl properly so called, 
that does not contain more than half its weight in calca¬ 
reous substances. 3. Clayey marl, that contains three or 
four times as much clay as marl. 4. Marly clay, that 
contains the feeblest portion of calcareous carbonate.* 
31. Marl can not always be recognised simply by the 
eye; to distinguish it, it is necessary to have recourse to 
the means indicated in treating of the mineral parts of the 
soil. 
32. The same error that prevents the use of lime also 
prevents that of marl, in many instances, when it should 
be used. It has been often used as a manure, when it 
should merely be considered an ameliorator. Whenever 
lime or marl is used upon a soil deficient in the proper 
quantity of organic remains, sc far from producing any 
effect upon the physical properties of the soil, it will be 
apt to injure by giving it too much activity. 
33. Marl, by its beneficent properties, should play an 
important part in the agriculture of many districts in the 
* There are many other varieties not necessary to describe. 
