CALCAREOUS MANURES— THEORY. 3J 



in poor land. No plant prefers poor to rich soil— or can tlirive better on a 

 scarcity of food, than with an abundant supply. Pine, broom-grass, and 

 sheep-sorrel, delight in a class of soils that are generally unproductive —but 

 not on account of their poverty ; for all these plants show, by the greater 

 or less vigor of their growth, the abundance or scarcity of vegetable matter 

 in the soil. But on this class of soils, no quantity of vegetable manure 

 could make locusts flourish, though they will grow rapidly on a calcareous 

 hill-side, from which all the soil capable of supporting other ordinary plants 

 has been washed away. 



In thus describing and distinguishing soils by their growth, let me not be 

 understood as extending these rules to other soils and climates than our 

 own. It is well established that changes of kind in successive growths of 

 timber have occurred in other places, without any known cause ; and a 

 difference of climate will elsewhere produce effects, which here would in- 

 dicate a change of soil. 



Some rare exceptions to the general fertility of shelly lands are found 

 where the proportion of calcareous earth is in great excess. Too much of 

 this ingredient causes even a greater degree of sterility than its total ab- 

 sence. This cause of barrenness is very common in France and England, 

 (on chalk soils,) and very extensive tracts are not worth the expense of 

 cultivation, or improvement. The few small spots that are rendered bar- 

 ren here are seldom (if ever) so affected by the excess of oyster or muscle 

 shells in the soil. These effects generally are caused by beds of fossil sea- 

 shells, which in some places reach the surface, and are thus exposed to the 

 plough. These spots are not often more than thirty feet across, and their 

 nature is generally evident to the eye ; and if not, is so easily determined 

 by chemical tests, as to leave no reason for confounding the injurious and 

 beneficial effects of calcareous earth. This exception to the general fer- 

 tilizing effect of this ingredient of our soils would scarcely require naming, 

 but to mark what might be deemed an apparent contradiction. But this 

 exception, and its cause, must be kept in mind, and considered as always 

 understood and admitted throughout all my remarks, and which therefore 

 it is not necessary to name specially, when the general qualities of calca- 

 reous earth are spoken of 



In the beginning of this chapter, I advanced the important fact that none 

 of our poor soils contain naturally the least particle of calcareous earth. 

 So far, this is supported merely by my assertion— and all those who have 

 studied agriculture in books will require strong proof before they can give 

 credit to the existence of a fact, wliich is either unsupported, or indirectly 

 denied, by all written authority. Others, who have not attended to such 

 descriptions of soils in general, may be too ready to admit the truth of my 

 assertion —because, not knowing the opinions on this subject heretofore re- 

 ceived and undoubted, they would not be aware of the importance of their 

 admission. 



It is true that no author has said expressly that every soil contains calca- 

 reous earth. Neither perhaps has any one stated that every soil contains 

 some silicious or aluminous earth. But the manner in which each one has 

 treated of soils and their constituent parts, would cause their readers to 

 infer that neither of these three earths is ever entirely wanting— or at least 

 that the entire absence of the calcareous is as rare as the absence of sili- 

 cious or aluminous earth. Nor are we left to gather this opinion solely 

 from indirect testimony, as the following examples, from the highest autho- 

 rities, will prove. Davy says, " four earths generally abound in soils, the 

 aluminous, the silicious, the calcareous, and the magnesian"*; and the soils 



* Davy's Agr. Chcm., Lecture 1. 



