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CHAPTER VII. 



NITROGENOUS MINERAL SUBSTANCES. 



There are some mineral substances admix- 

 ed with nitrogenous matters used as manures; 

 for instance, shells, river or swamp muck, 

 and the saltpetre earths of all the provinces. 

 The sea sand used in Brittany is called merl. 

 The merl is a muck filled with shells and ani- 

 mal matters, from which it derives its princi- 

 pal properties. It is found abundantly at the 

 mouth of the river Morlaix, whence it is 

 drawn up by a drag. The roadstead of Brest 

 and the river Quimper, also yield large quan- 

 tities. The harvest of merl is made from Ma}^ 

 fifteenth to October fifteenth in lighters, the 

 contents of each of which (16,000 pounds,) 

 sells for 80 cts. to ^1.00. This manure should 

 be used soon after it is taken from the water, 

 for it rapidly disintegrates in the air and par- 

 tially loses its properties. Merl, by reason of 

 its calcareous matter, is peculiarly fitted for 

 argillaceous soils. According to Payen and 

 Boussingault, the Morlaix merl contains in a 

 dry state, 0.12 per cent, of nitrogen. Fresh 

 from the see, it contains one-half its weight 



