308 A. Winchell on the Saliferous Rocks of Michigan. 



actually been strengthened by the loss of more water than it has 



The subterranean basins of Michigan furnish us with three 

 " great salt lakes." The principal one of these is shown, for the 

 first time, in the " First Biennial Eeport" of the geology of the 

 State (1860), to occupy a position between the Carboniferous lime- 

 stone and the sandstones at the base of the Carboniferous system 

 —being on a parallel with the gypsiferous formation of Nova 

 Scotia. It is a mass of argillaceous, gypseous and pyritous 

 shales, with thin beds of arenaceous and magnesian limestone, 

 and beds of pure gypsum from eleven to twenty feet in thickness. 

 The aggregate thickness is from 180 to 200 feet. Its outcrop de- 

 scribes an irregular circle, embracing the central portion of the 

 peninsula. It underlies an area of 17,000 square miles, em- 

 bracing the whole of 19 counties and at least half of 16 others. 

 This assemblage of strata, though probably inchided in the 

 American representation of the Mountain Limestone of the Old 

 World, has received the local designation of Michigan bait 



Seven hundred and fifty feet below this is the Onondaga salt 

 group, the circuit of whose outcrop is traced from Monroe 

 county to Gait in Canada West, thence to Mackinac island, M»- 

 waukie and southward. The supply of brine in these strata Has 

 not been ascertained. They are well stocked with gypsuna ana 

 are known to be saliferous, . i 



The third saliferous horizon has but recently been recogniz^ 

 It was indeed known that brine of feeble strength exists m toe 

 coal measures, but only within a few days has it been proveu 

 that the salt wells at Bay City and vicinity on the Saganaw 

 river, are supplied from this source. It might have been kno^^^'^ 

 from the first existence of these wells, if those having the ■ 

 in charge could have been induced to preserve specimen? ■ 

 rocks. The Parma sandstone below the coal measure? 

 reservoir of this brine, as the Napoleon sandstone beric-;.^ 

 Michigan salt group is the reservoir of the brine from tin? ^ ^^^ 

 It is now known that the Bay City wells terminated at ^"^ .'j^ 

 torn of the Parma sandstone though bored to nearly as grca 

 depth as the wells of East Saginaw and vicinity, which \>^^^^^ 

 the Napoleon sandstone. This fact being established, a nevr 

 near Bay City has been sunk to a greater depth, and at 910 ^^^ 

 the Napoleon sandstone has been struck as predicted ; a/J^' 

 the depth of 74 feet in this rock, brine has been ^^'^''o^l^,^ 

 completely saturated. This occurrence, no less than the s'lCC'; ^ 

 of the first well bored in the valley, becomes a very gwti.>" - 

 confirmation of geological inferences drawn from obse!\ 

 extended over thousands of square miles, and in gro-^' 

 hundreds of miles distant from the points where success H:- 

 attamed. 



