SOMETHING ABOUT ROCK-SALT AND GYPSUM. 393 



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

 cules. 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- 



South, 



Novlfc 



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

 Report for 1867), showing the ancienf 

 group, now filled with gravel and cla; 

 from the old stump of the formation. 



Report for 1857), showing the ancient excavation of the outcrop of the Salina 

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



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 



