220 . THE EXHAUSTION OF CALXED LAND. 



eternal duration of a manure. But it can scarcely be believed 

 that the effect of any temporary manure, would not have been 

 somewhat abated by such a course of severe tillage. Under milder 

 treatment, there can be no doubt that there would have been much 

 greater improvement. [1842.] 



If subjected to a long course of the most severe cultivation, a 

 soil could not by such course alone be deprived of its calcareous 

 ingredient, whether natural or artificial : but though still calcare- 

 ous, it would be, in the end, reduced to barrenness, by the exhaus- 

 tion of its vegetable matter. Under the usual system of exhaust- 

 ing cultivation, marl certainly improves the product of acid soils, 

 and may continue to add to the previous amount of crop, for a 

 considerable time ; yet the theory of its action instructs us, that 

 the ultimate result of marling, under such circumstances, must be 

 the more complete destruction of the land, by enabling it to yield 

 all its vegetable food to growing plants, which would have been 

 prevented by the continuance of its former acid state. An acid 

 soil yielding only five bushels of corn may contain enough food for 

 plants to bring fifteen bushels ; and its production will be raised 

 to that mark, as soon as marling sets free its dormant powers. But 

 a calcareous soil reduced to a product of five bushels, can furnish 

 food for no more ; and nothing but an expensive application of 

 putrescent manures can render it worth the labour of cultivation. 

 Thus it is, that soils, the improvement of which is the most hope- 

 less without calcareous manures, will be the most certainly im- 

 proved with profit by their use. 



CHAPTER XXIII. 



GENERAL OBSERVATIONS ON THE VALUATIONS OF LANDS AND 

 THEIR IMPROVEMENTS, AND THE EXPENSES AND PROFITS OF 

 MARLING. 



PROPOSITION 5 concluded. 



At this time there are but few persons among us who doubt the 

 great benefit to be derived from the use of marl; and many of 

 those who formerly deemed the early practice the result of folly, 

 and a fit subject for ridicule, now give that manure credit for vir- 

 tues which it certainly does not possess ; and, from their manner 

 of applying it, seem to believe it a universal 'cure for sterility. 

 Such erroneous views have been a principal cause of the many 

 injudicious and even injurious applications of marl. It is as 



