SOMETHING ABOUT ROCK-SALT AND GYPSUM. 299 



Fig. 91. Section from East to West across the lower peninsula of Michigan. 



1, 2, 3, 4, 5, 6, etc. The several groups of strata from the Coal-measures to the 



Lower Silurian. 



will suffer the diluting influence of surface waters only 

 around the outcropping borders. Fresh water will float 

 as a distinct stratum upon a stratum of strong brine. The 

 deepest parts of a saliferous formation must consequently 

 contain the strongest brine. The place of salt springs will 

 naturally be along the outcropping belt of the formation. 

 They are the mere overflow of the basin caused by surface 

 rains. The region over the most depressed portion of the 

 basin, and consequently over the deposit of strongest brine, 

 is likely to be completely destitute of salt springs. The 

 position of the brine-supply is therefore a problem for 

 strictly geological determination. It is an induction from 

 the general geology of the entire region. Superficial inves- 

 tigators have frequently instituted borings in the vicinity 

 of brine springs. Inevitably such explorations must imme- 

 diately pass below the source of brine-supply, and must 

 prove unsuccessful, unless they can be extended to some 

 more deeply seated basin, whose outcropping rim is com- 

 paratively remote. The most successful salt wells are those 

 which are bored far from surface indications, in places 

 pointed out by geology as located over the central portion 

 of a saliferous basin. 



From the conditions of the case, it is almost a hydrostat- 

 ical impossibility that a good brine well should be a flow- 

 ing well. The strong brine must be pumped up from the 

 bottom. It may be asked why, if the borders of the basin 



