304 SKETCHES OF CREATION. 



of the brine is gradually diminishing. The same formation 

 affords brine and gypsum in the vicinity of the Grand Riv- 

 er of Ontario, and rock-salt and strong brine at Goderich. 

 It is worked for gypsum in the vicinity of Sandusky, Ohio. 

 It underlies the whole of the lower peninsula of Michigan 

 (Fig. 91) in the form of a vast basin, whose borders come 

 to the surface at Milwaukee on the west, Mackinac on the 

 north, the Grand River of Ontario on the east, and Sandus- 

 ky on the southeast. This great salt basin has been pene- 

 trated, under the guidance of geology, at St. Clair and at 

 Point aux Barques, and successful wells eleven hundred 

 feet deep are now in operation. A new well is about to 

 be put in operation at Mount Clemens, in Macomb County, 

 and others are in progress at various points. 



The next saliferous formation, in ascending order, is one 

 which is peculiar to the lower peninsula of Michigan, and 

 has hence been styled the "Michigan Salt Group." Its 

 geological position is between the Marshall sandstone 

 and the Mountain limestone. It underlies, like a great 

 dish, nearly the whole of the peninsula. Its outcropping 

 rim is marked by a circuit of salt springs. Filtration has 

 leached out most of the brine into the underlying sand- 

 stones. The gypsum, however, mostly remains in the for- 

 mation, and is extensively worked. The wells of East 

 Saginaw and Saginaw City are supplied from this forma- 

 tion. As in the case of the Salina basin, this one is reached 

 by deep borings over the most depressed portion (Fig. 91). 

 These borings were originally undertaken as the result of 

 a pure geological induction, and strong and copious brine 

 was obtained at the depth of about eight hundred feet. 

 The first rock, even, was one hundred feet from the sur- 

 face, and the whole thickness of the Coal-measures had to 

 be crossed. I consider such successes ample vindication 

 of the utility of geological science. The geological sur- 



