lOO LOWER PENINSULA. 



feet of a shale formation are found before the deeper massive sand 

 rock beds arc struck, which latter, in the technical language of the 

 salt manufacturer, arc called the salt rock, because they supply him 

 with strong, valuable brine. The brine is not confined to a certain 

 horizon in the Waverly group ; it seems to pervade all of it, but 

 has accumulated only in beds sufficiently porous to absorb it from 

 the surrounding rock mass, and sufficiently protected from the 

 percolation of surface waters to retain the solution of the salt in 

 concentrated form. These conditions are much better fulfilled 

 by the deeper beds than by the more superficial. In the majority 

 of salt wells, high above the productive level, there is found 

 a weak brine which increases in strength the nearer we come to 

 the principal, more deeply situated repository. Experience has 

 taught the salt manufacturer that, after exhaustion of the first 

 salt rock, by boring deeper, sometimes, but not always, another 

 sand rock saturated with strong brine can be found, termed by 

 him the second salt rock ; but this designation is not applicable 

 to a rock having a certain geological position, as it relates only to 

 the conditions of a locality, and as the equivalent of the second 

 salt rock in one well may be in another the upper or first salt rock. 



In the salt wells of Tawas, Caseville, Port Austin, Port Hope, 

 White Rock, etc., the salt rock is inclosed by the deeper shaly divi- 

 sion of the Waverly group. The upper strata of the formation, as 

 the sandstone of Point of Barques, and the grindstones, contain no 

 salt in these localities ; they have been leached out owing to their 

 superficial position. The salt wells of Saginaw, on the other hand, 

 seem to furnish their supply of brine from the upper sand rocks cor- 

 responding to the Point of Barques sandstone or the grindstones. 

 They are deeply buried under the coal measures and the carbonife- 

 rous limestone, which prevent the atmospheric waters from perco- 

 lating through them. The brine contained in these beds even rises 

 into the superincumbent layers of the coal series, with the waters 

 circulating below it, which all are under a certain hydrostatic 

 pressure driving them upward to the surface. 



From all the facts known, we must suppose that the salt exists 

 in the strata as a solution, retained in the porous sand rock as in a 

 sponge. Indications of solid rock salt have never been noticed in 

 any of the salt wells of Saginaw district. I have stated that brine 

 is found in almost every part of the State where the Waverly 



