53 o VARIOUS FERTILITY FACTORS 



less soluble salts, such as (i) calcium sulfate (gypsum) and (2) 

 sodium chlorid (common salt), begin to separate in crystals which 

 settle to the bottom; and with further evaporation of water the 

 more soluble salts of potassium and magnesium finally separate 

 in crystals which are deposited in strata above the principal salt 

 deposits. 



After vast amounts of water had been evaporated and immense 

 quantities of salts deposited, these accumulations sometimes be- 

 came covered with drift material (clay etc.) several feet in thick- 

 ness, and at a later period the sea water again came in and by 

 evaporation left a second, stratum of calcium sulfate, and above it 

 another immense salt deposit. 



The total thickness of these various strata is about 5000 feet 

 at Stassfurt. There are many variations and irregularities, but 

 in the main the lower stratum consists largely of calcium sulfate; 

 next above is the sodium chlorid deposit of great depth; then a 

 layer of the mineral polyhalite, composed of the sulfates of po- 

 tassium, calcium, and magnesium, kieserite (magnesium sulfate), 

 and finally a stratum varying from 50 to 130 feet in thickness, 

 which consists largely of carnallite, a double salt of potassium and 

 magnesium chlorid. 



In some places the overlying clay or earth became cracked, and 

 water entered from the surface, so that more or less of the various 

 salts were dissolved and redeposited in veins or pockets in com- 

 pounds or forms not commonly found in the more general strata. 

 Thus were formed comparatively small beds of kainit, sylvanite, and 

 hartsalz. More than thirty different compounds or minerals are 

 found in these Stassfurt deposits, and at least a dozen of these 

 contain more or less potassium. 



By far the most abundant source of potassium is the carnallite 

 stratum, but even the pockets or beds of kainit, sylvanite, and 

 hartsalz are of great importance. The following are commonly 

 accepted as the formulas which represent these minerals: 



Carnallite, KC1 MgCl 2 6 H 2 O. 



Kainit, K 2 SO 4 MgSO 4 MgCl 2 6 H 2 O. 



Sylvanite, K 2 SO 4 MgSO 4 KC1 MgCl 2 NaCl 6H 2 O. 



Hartsalz, KC1 MgSO 4 NaCl H 2 O. 



