166 REPORT OF THE 



produce brine of sufficient strength for manufacturing purposes; 

 ai.d a [». esci t only the Gypseous Group is known to do this. 

 4 Bef .re deciding on the indications of a salt spring, there- 

 fore, it is necessary to know from what geological foimation it 

 issues. Here the elaborate investigation of the order and dis- 

 tribution of (mi - st au, finds one of its applications. 



5. Before the origin of the brine can be known, we must as- 

 certain whether it flows out horizontally at an outcrop, or rises 

 vertically through fissures in strata overlying the salt rock. A 

 fundamental mistake, committed in the early explorations for 

 salt, grew out of the assumption that the brine of our springs 

 generally rises through fissures, and may be sought by boring 

 in the vicinity of the springs. 



6. Most of our springs issue at outcrops of saliferous strata; 

 so that the moment we brgiu to bore in such situations, we find 

 ourselves beneath the source of the salt. 



1. The source of the salt must be sought by traveling from 

 the spring toward the center of the basin, when, by boring 

 down, the brine may be expected in increased strength and 

 quantity. 



8. Our saliferous basin extends from Grand Rapids to Sanilac 

 county, and an uuknown distance toward the north. Within 

 this basin, the area covered by the Coal Measures may be taken 

 as the area underlain by saliferous strata of maximum produc- 

 tiveness. 



A great deal of enterprise has been manifested in the estab- 

 lishment of the salt manufacture at Grand Rapids, and a fair 

 degree of success may yet be anticipated. This location is, 

 however, within three or four miles of the outcrop of the salife- 

 rous strata, and I have all along thought and stated that the 

 prospects were less encouraging than they would be farther 

 within the basin. The salt bearing strata lie here about* 200 

 feet from the surface; but those who have been engaged in this 

 enterprise have been loth to shake off the old illusion that the 

 great reservoir of the salt lies at the depth of six or eight hun- 

 dred feet. They have, therefore, in nearly every case, persisted 



