CAUSE OF THE NON-ACTION OF GYPSUM. 147 



other, and was not mowed at all the last year, being thin and low, 

 and almost eaten out by wire-grass (Cynodon dactylon). 



1826. In corn and it was remarkable that the difference shown 

 the last year was reversed, the mussel-shell marling now having 

 much the best crop. 



In these and other applications to neutral soils, I ascribe the 

 earliest effects entirely to gypsum, as well as the peculiar benefit 

 shown to clover, throughout. The later effects, and especially on 

 grain, are due to the calcareous earth in the manure. 



CHAPTER XVII. 



DIGRESSION TO THE THEORY OF THE ACTION OF GYPSUM AS MA- 

 NURE. SUPPOSED CAUSE OF ITS WANT OF POWER AND VALUE 

 ON ACID SOILS. 



PROPOSITION 5 continued. 



ANOTHER opinion was formed from the effects of gypseous marl, 

 as stated in the foregoing chapter, which may lead to profits much 

 more important than any to be derived from the limited use of this, 

 or any similar mineral compound viz. : that gypsum may be pro- 

 fitably used after calcareous manures, on soils on which it was 

 totally inefficient before. I do not present this as a fact fully esta- 

 blished, or, even if established, of universal application ; for the 

 results of some of my own experiments are directly in opposition. 

 But, however it may be opposed by some facts, the greater weight 

 of evidence, furnished by my experiments and observations, de- 

 cidedly supports this opinion. If correct, its importance to our 

 low country is inferior only to the value of calcareous manures 

 alone which value may be almost doubled, if the land is thereby 

 fitted to receive the wonderful benefits of gypsum on clover. 



It is well known that gypsum has failed entirely as a manure on 

 nearly all the land on which it has been tried in our tide-water 

 district; and we may learn from various publications, that as little 

 general success has been met with along the Atlantic coast, as far 

 north as Long Island. To account for this general failure of a 

 manure so efficacious elsewhere, some one offered a reason, which 

 was received without examination, and which is still considered by 

 many as sufficient, viz. : that the influence of salt vapours ^destroyed 

 the power of gypsum on and near the sea-coast. But the same 

 general worthlessness of that manure extends one hundred miles 

 higher than the salt water of th^ rivers, and the lands where it is 



