542 GEOLOGY 



The Cayugan (Salina) series. The Salina formation, which 

 overlies the Niagaran in parts of New York, Pennsylvania, Ohio, 

 Michigan, and Ontario, is much less widespread, and its limited 

 distribution points to the emergence of a considerable area in the 

 Mississippi basin at the close of the Niagaran epoch. 



The Salina series embraces several varieties of rock, including 

 conglomerate, sandstone, limestone, shale, and rock salt. Witli 

 these formations, some gypsum, the usual accompaniment of salt 

 beds, is associated. Shale is the most abundant, and seems to have 

 originated after the fashion of shales in general, but the fewness of 

 its fossils seems to point to deposition under conditions unfavorable 

 for life. 



The salt is widely distributed. It occurs at many points in New 

 York within an area 9,000 to 10,000 square miles in extent. Single 

 beds of it are locally 40 to 80 feet thick. Several beds sometimes 

 occur one above another, interstratified with other sorts of rock, 

 and their aggregate thickness sometimes reaches as much as 100 

 feet. Near Cleveland, four salt beds, 50 feet and less in thickness 

 are interstratified with 500 feet of shales. In some places, there- 

 fore, the salt makes a very considerable fraction of the total thick- 

 ness of the series. 



The salt beds seem to imply the existence of great lagoons or 

 inclosed seas, in which the Salina series was deposited. Had the 

 climate of this region been as moist as now, these lagoons could not 

 have been abnormally saline. 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 when they 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. A bed of salt 40 feet thick implies the evaporation of sonic 

 3,000 feet of normal sea-water. Much of the salt of commerce 

 which comes from New York is not derived immediately from the 

 salt beds, but from the waters of salt wells. 



The limestone of the Salina proper is largely contemporaneous 

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



