SOILS AND MANURES. 361 



does good service often in aiding the weathering (491) of 

 the mineral substances in the soil, and thus acts as a sol- 

 vent for matters which the plants need but can not get un- 

 less they are dissolved. The direct manures, you observe, 

 act with their own power, and furnish some of their own 

 material to plants ; but lime, on the other hand, does not 

 work with its own material, but at the expense of other 

 matters in the soil. Lime, therefore, tends eventually to 

 make the soil poorer unless other manures are applied at 

 the same time, and hence the maxim current among the 

 Belgian farmers : 



"Much lime and no manure 

 Makes both farm and farmer poor." 



504. Marl. "VYe have alluded to this manure in 493. 

 Marl is a lime mud which was deposited in the last over- 

 flowings of the surface of the earth in its preparation for 

 man. It is sometimes tolerably pure, but is commonly 

 mingled with clay, stones, shells, etc. The lime in it is in 

 the form of carbonate. Its effects upon soils are very 

 similar to those of quick-lime, just described. There are, 

 however, other substances mingled with the carbonate of 

 lime, which modify its effects, and render the marl more 

 valuable as a fertilizer than it otherwise would be. Yet 

 these are so small in amount that the Belgian proverb is 

 nearly as true of marl as it is of lime. 



505. Gypsum. The fertilizing properties of sulphate of 

 lime were known in Europe long before they were in this 

 country. Franklin, when abroad, was struck with the rich- 

 ness of the crops raised in fields manured with gypsum, and 

 endeavored to persuade American farmers to use it, but in 

 vain. To convince them of the truth of his statements he 

 resorted to the following expedient : He strewed gypsum 

 on a sloping field in such a way as to form in enormous 

 letters the words Effects of Gypsum. The abundant growth 



Q 



