166 MARL : ITS NATURE AND EFFECTS. 



atmosphere ; in other words, it is not dissolved, or de- 

 composed, or changed, by the ordinary atmospher 

 agents which react so powerfully upon many other 

 minerals ; and consequently we are to regard it as near- 

 ly impossible to effect its decomposition by the vital 

 power of their organs, and imbibe a portion of its con- 

 stituents. 



" Mr. Wooley manured a piece of land in the propor- 

 tion of two hundred loads of good stable-manure to 

 the acre, applying upon an adjacent tract of the same 

 soil his marl, in the ratio of about twenty loads per 

 acre. The crops, which were clover and timothy, were 

 much the heaviest upon the section which had received 

 the marl ; and there was this additional fact greatly in 

 favor of the fossil manure over the putrescent one, 

 that the soil enriched by it was entirely free of weeds, 

 while the stable-manure rendered its own crop very 

 foul. 



" This being an experiment, an extravagantly large 

 dressing of manure was employed, but not exceeding 

 the usual average application : more than twenty loads 

 of marl surpassed what was necessary for it. 



" Experience has already shown that land, once 

 amply marled, retains its fertility, with little diminution, 

 for at least ten or twelve years, if care be had not to 

 crop it too severely ; while, with all practical precau- 

 tions, the stable-manure must be renewed at least three 

 times in that interval, to maintain in the soil a corre- 

 sponding degree of vigor. 



" A specimen of the marl from Thorp's lowest layer 

 yielded me, after reiterated trials, uniformly about the 

 following for its composition : 



In 100 Grains. 



Silica, 43.40 



Protoxide of iron, . 21.60 



Alunrni, 6.40 



Lime, 10.40 



Potash, 14.48 



Water, - 4.40 



99.68 



