SOMETHING ABOUT EO CK- SALT AND G YPS UM. 303 



rise or sink into the spaces between isolated gypsum-lenti- 

 cnles. 5. Gypseo-saliferous formations are generally of lo- 

 cal extent in one direction or in both, indicating that they 

 were accumulated in a restricted portion of the ocean. 



The productive salt formations of the United States are 

 three. The Salina group is the source of supply of brine 

 and gypsum to Onondaga and Cayuga Counties, New York. 

 The vast manufacture of the Empire State is based upon 

 this supply. Only the northern rim of the basin or forma- 

 tion is known (Fig. 92). Its outcropping edge was deeply 

 excavated by the agencies of the ice-period, and the excava- 



SoutK 



North 



Fig. 92. Longitudinal section of the Onondaga Salt Basin (from Superintendent's 

 Report for 1S5T), showing the ancient excavation of the outcrop of the Salina 

 group, now filled with gravel and clay, and saturated by an exudation of brine 

 from the old stump of the formation. 



tion was filled with gravel. The overflow from the notched 

 rim of the basin saturates the gravel, and thus forms a vast 

 inland salt-marsh. The strongest brine settles to the bot- 

 tom of this basin, and is reached by wells of the ordinary 

 kind, and pumped out. It seems inevitable that a supply 

 obtained under such geological circumstances must be lia- 

 ble to rapid exhaustion. The facts show that the strength 



