82 MARL. 



and lime are blended in certain proportions. Wheat 

 cannot grow in a soil destitute of, or deficient in, cal- 

 careous matter, which is generally more or less the 

 case with sandy land. Gypsum, or Plaster of Paris, 

 is sometimes used. It is a sulphate of lime, or sulphu- 

 ric acid (oil of vitriol) combined with lime. The 

 lime binds the sand, and the sulphuric acid is a stimu- 

 lus, and serves to attract moisture from the atmos- 

 phere, which, when covered, serves to enrich the 

 soil. 



Clay lands are denominated cold, because they are 

 of a compact, solid texture, resisting more than sand 

 the action of the sun's rays. The roots of plants 

 cannot penetrate such a soil freely, and like all so- 

 lid bodies its temperature is low, being too cold to 

 carry on the process necessary to the health and ra- 

 pid growth of plants. It is here that the stone or 

 sand marl is beneficial, in rendering the soil more po- 

 rous, by which heat and moisture are admitted to as- 

 sist in digesting the food necessary to the growth of 

 the plant. 



It is a very easy matter to distinguish marl from 

 mere clay, and also to discover whether it is marl or 

 not. Put a piece or a portion pulverized into one of 

 the acids, even vinegar, if strong, and if effervescence 

 takes place, it is an evidence sufficient that it is marl, 

 for clay will not effervesce in any of the acids. The 

 effervescence is occasioned by the action of the acid 

 on the lime contained in the marl. 



