Chalk (Marne) 



by the gypsum. It is known that gypsum clover 

 is difficult to dry. Until final experiments have 

 decided the real value of gypsum in agriculture, it 

 would be better not to popularise its use. Under 

 no circumstances should it be used for cereals, or 

 in ground that lacks humus. Gypsum can be 

 economically supplied by means of superphosphates, 

 in which about 50 per cent, is present. This 

 explains the favourable action of superphosphates 

 on some deep-rooted crops. 



Chalk (Marne). 



Chalk is really a mixture of clay and calcaire ; 

 dolomite or sand often being found in it. 



Chalk swells and disintegrates under the action 

 of air and moisture. It is easily recognisable be- 

 cause when worked upon by strong vinegar it be- 

 comes effervescent. 



The composition of chalk is very variable. It 

 contains more or less limestone, clay, sand or 

 dolomite. 



One meets at all depths. When near the surface 

 its presence is revealed by characteristic vegetation, 

 such as coltsfoot, thorns, thistles, plantains, etc. 



It is divided into upper and lower chalk ; these 

 differ in nature and in quantity, and consequently 

 the soils deriving from them differ also. It is chiefly 

 in the upper chalk that one finds flint beds ; this 

 chalk is white although the surrounding soil is often 

 black, by mixture with a part of the uppermost 

 stratum laid bare by erosion, or because of the 

 accumulation of organic matter. These soils are 

 easily cultivated, being rather light ; though poor, 



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