388 GEOLOGY. 



of the present time, these lagoons would hardly have become abnor- 

 mally saline. The fact that salt was precipitated in such quantities 

 is therefore an indication of aridity. Data are not at hand for deter- 

 mining whether the aridity was local or general. Whenever and where- 

 ever the water of these inclosed seas reached the saturation-point 

 for salt, its precipitation began. Occasional incursions of the sea, 

 bringing in new supplies of salt water, followed by periods when the 

 lagoons were cut off from the sea, and suffered rapid evaporation, 

 would seem to meet the conditions demanded for the formation of 

 the salt. So also would a slight continuous connection with the sea, 

 such that the inflow of sea-water into the basin did not balance the 

 excess of evaporation over precipitation in the basin area. Beds of 

 salt 40 to 80 feet thick imply the evaporation of 3000 to 6000 feet of 

 normal sea- water. 



It is not known how nearly continuous the beds of salt are in the 

 area within which they occur. Knowledge concerning them is obtained 

 only from borings, for they are buried beneath great thicknesses of 

 younger rock. Since the strata dip to the south, the salt beds lie 

 farther and farther beneath the surface in that direction. Much of 

 the salt of commerce which comes from New York is not derived imme- 

 diately from the salt beds, but from the waters of salt wells. The 

 water of these wells probably became briny by passing over or through 

 the salt beds, or over or through strata of shale through which salt is 

 disseminated. 



Gypsum is often associated with sedimentary formations deposited 

 in inclosed seas. It is much less soluble in waters which are nearly 

 saturated with salt than in sea-water. Since it is usually present 

 in saline waters, it is likely to be precipitated as the water approaches 

 the saturation point for salt. In keeping with these general facts, 

 it is present in the Salina series. Some of the gypsum is probably of 

 secondary origin, being the result of the reaction of sulphuric acid on 

 calcium carbonate. 



The limestone of the Salina proper is largely contemporaneous with 

 the shales and salt beds. It is thickest where they are thin, and thin 

 where they are thickest. It contains few fossils, and may be a chemical 

 precipitate. Its relations to the shales and salt beds are such as to 

 indicate that the areas of accumulation of the several sorts of rock 



