186 PROCEEDINGS OF THE ACADEMY OF [1<S88. 



hand the saltpetre fields of Tai'apaca and Ataeania in Chile, now 

 resting on lower levels to those of the original salt-pans, afford an 

 example of an entire series of beds. In the reopening of the bar in 

 the Stassfurt basin, the process of salt deposition came again into 

 operation above the stratum of clay protecting the mother-liquor or 

 Abraum-solts ; this is proved by the occurrence of an upper salt bed, 

 with anhydrite-cap etc. 



The lowest division of the whole series there, though the name 

 does not correspond very well, is known as the Anliydrltregion, or 

 zone of anhydrite, on account of thin j^arallel bands of sulphate of 

 lime transversing it at regular intervals ; they are called annual rings 

 (Fahresringe), but cannot be explained by the direct influence of 

 the seasons, e. g. in winter, because they are not found in other salt 

 deposits, which have been formed under similar climatic conditions. 

 It is more probable that a process, similar to that in the dej^osition 

 of the second lot of calcium carbonate of Usiglio, has taken place in 

 their formation. Some agent or other, related to that, which caused 

 the conversion of gypsum and soda into carbonate of lime and sul- 

 phate of soda, must also have been at work here. Most likely the de- 

 composition took place at first gradually, whereas towards the end 

 it was rapid, from which can be explained the " rings " being ramified 

 below and level above. Local peculiarities may also have been the 

 cause, for instance, periodic supplies of water coming from the land, 

 but it was certainly not of a purely climatic nature. This might 

 be a probable explanation for the exceptional case of Stassfurt de- 

 posits, where the mother-liquors were dried uj) above the salt beds 

 proper and not afterwards removed by external agencies. 



As the process of filling up of a salt-pan with gyj^sum, rock-salt, 

 anhydrite and salt-clay has proceeded so far that the anhydrite-cap 

 reaches the height of the bar, the latter deposit naturally retains 

 cavities and irregularities in its surface, occupied by fluid residues 

 of mother-liquors. These residues must often have been pretty consider- 

 able, and they represent a most important geological agency ; for 

 rock-salt formations can only occur on the sea-coast, and it is here 

 that volcanic action has its sway, so that we often find the neptunis- 

 tic and volcanic forces cooperating. Through displacement in the 

 beds, the residual mother-liquors are set free and flow to lower levels, 

 where on reaching an impervious stratum they collect and form a 

 salt-lake ; or if brought to the surface again appear as brine and 

 mineral springs more or less removed from the original source. 



