1888.] NATURAL SCIENCES OF PHILADELPHIA. 185 



sium compounds, and hence causes a degeneration in the marine 

 fauna and flora on the East coast. The Oxus (Amu Darja), which 

 two centuries ago poured its waters into Adschi Darja prevented a 

 deposition of salt there, hut since sand-storms have diverted this 

 stream into the Aral, the change of the Caspian into a bitter-lake 

 has been accelerated by the formation of sand-bars along the East- 

 coast bays, which are converted into salt-pans. 



The above description of the processes now being carried out on 

 the East coast of the Caspian will suffice to illustrate the origin of all 

 rock-salt deposits, from the Silurian down to the present era, and 

 further, the occurrence in each of gypsum, as basis and the Anhydrite- 

 cap with salt-clay as cover. Fossils are hardly ever present, and 

 mother-liquor salts rarely in large amounts. 



To go back to the time when the first signs of the anhydrite-cap 

 make their apjjearance, we find that an increase in altitude of the 

 bar, sufficient to cut off" the influx of sea-water, causes the mother- 

 liquors to stagnate and under favorable conditions of temperature to 

 solidify. Such a process has taken place in the Egeln-Stassfurt ba- 

 sin, and in some other localities of the old North-German Permian 

 salt-sea. The potassium and magnesium salts, together with boron 

 and bromine compounds, have crystallized out and been exception- 

 ally well protected against re-solution by a clay seam imj^ermeable 

 to water. There are to be seen lying on a rock-salt bed many hun- 

 dred yards thick, consecutive zones of carnallite, kieserite and poly- 

 halite ; the latter generally encloses the sulphate of lime, which was 

 still contained in the waters of the bay at the time of the closing in' 

 by the bar, magnesium sulphate occurs especially in the second, and 

 in the zone of carnallite are found the chlorides of magnesium and 

 potassium, borates and magnesium calcium bromide (brom-car- 

 nallite). Calcium chloride is also met with in certain minerals, 

 such as tachhydrite etc., and in some cases undergoes in presence of 

 magnesium sulphate a double decomposition, calcium sulphate and 

 magnesium chloride being formed. 



The total quantity of chloride of magnesium occurring in the 

 Stassfurt beds does not correspond to the normal amount ; portions 

 of this substance must have made their exit over the bar with the 

 lithium and iodine salts, or have been absorbed by the upper beds 

 (N. B. lithium is found in the salt-clays above, but not iodine) or 

 were carried away in solution later on. Hence the succession of 

 mother-liquor salts in Stassfurt is not quite complete ; on the other 



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