298 SKETCHES OF CREATION. 



vation. On the other hand, it may have been subjected to 

 a depression of such an extent that the region became 

 again the site of the open sea; and sediments of later date 

 were accumulated upon the top of strata inclosing rock- 

 salt and gypsum. 



The preservation of the saline constituents of a formation 

 thus originated must be conditioned on the vicissitudes to 

 which it was subsequently subjected. It is obvious that 

 the original conformation of the saliferous strata must have 

 been somewhat dish-like or depressed in the centre, with 

 the borders elevated. In the uplift of the continent, all 

 portions may have been simultaneously raised, or the for- 

 mation may have become decidedly tilted. In the filtra- 

 tion of surface waters through the interstices of the strata, 

 it is obvious that any formation so posited as to permit a 

 flow of water through it, either vertically or laterally, must 

 have all its soluble constituents dissolved out. A vertical 

 leaching may simply transfer these constituents to some 

 lower formation underlaid by an impervious floor. A lat- 

 eral drain may discharge the soluble contents at the sur- 

 face of the earth, and thus, by degrees, restore them to the 

 ocean, their ancient home. Hence many strata now desti- 

 tute of either salt or gypsum may have embraced both at 

 the time of their origin. In others we witness these sub- 

 stances — especially the gypsum — in process of disappear- 

 ance. 



In case the gypseo-saliferous formation has retained its 

 centrally depressed conformation (compare Fig. 91), it is 

 apparent that the saline constituents held must be unable 

 to escape by drainage. Surface waters will fall upon the 

 belt of outcrop of the formation, and may find their way to 

 the interior in sufficient quantity to redissolve the soluble 

 matters. This having been done, however, the saturated 

 solution will charge the interstices of the formation, and 



