214 
ECONOMIC GEOLOGY 
In the Salz-Kammergut in Eastern Austria tongues of salt 
project into clays like igneous intrusions, and the clays 
around have been disturbed and moved by the entrance 
of the salt. The salt was apparently deposited in the area 
by evaporation, and during subsequent earth-movements 
some of it was dissolved and redeposited in tongues, which 
as they grew forced their way into the shales. 
Porasu SALTs 
VALUE 1v AcricuLTurE—Potash is indispensable in 
agriculture as a fertilizer, owing to the amount which is 
removed from the soil in each crop. A wheat crop of 30 
bushels to the acre removes 28 Ib. of potash, a hay crop of 
14 tons to the acre 56 Ib., a 6-ton crop of turnips 78 Ib., and 
a 22-ton crop of mangels 3001b. The potash in soils is mainly 
derived from the felspars and felspathoids. The potash 
in these minerals occurs as a silicate; during weathering it 
is dissolved as bicarbonate and carried by rivers to the sea. 
In the Thames at Kew 1} per cent. of the dissolved matter 
in the water is potassium, and there is 1 1b. of potassium in 
every 00 tons of water. Waters which flow directly from 
areas of felspathic rock contain larger amounts. Potassium 
amounts to 6-71 per cent. of the salt in the Eger, a tributary 
to the Elbe in Saxony, and to 4 per cent. in Lac de Champex 
in the Valais in Switzerland. 
DEerivED FROM Sea-WateErR—Potassium occurs in the sea 
as sulphate and chloride ; some of it is deposited as glauconite, 
which colours greensand : some potash is extracted by sea- 
weeds, of which the burnt ash or * kelp.~was formerly the 
chief source of supply. 
Potassium chloride, owing to its extreme solubility, re- 
mains in evaporating sea-water until the water has been al- 
most completely removed. Potash chloride collects in such 
lakes as the Dead Sea. When such waters are completely 
evaporated their potash is deposited as one of a series of 
sulphates or chlorides. The first potash is precipitated as a 
sulphate, such as glaserite (K,SO,), which may be associated 
with the other simple sulphates, kieserite (MgSO, H,0), 
glauber salt (Na,SO,), and anhydrite (CaSQ,), and also with 
such double sulphates as glauberite (sulphate of calcium and