STATE GEOLOGIST. 165 



ping, 15,000 cubic yards having been already excavated, and 

 1,200 tons of plaster taken out from a bed 12 feet thick. At 

 the present time from 60 to 100 tons are quarried per day. 



The amounts of gypsum received at Detroit during the past 

 year are as follows: 



Tons. 



From Grand Eapids, 6,030 



" Sandusky, , 4,661 



Total 10,691 



Unless gypsum should be discovered in Monroe county, the 

 region along the Southern railroad will continue to be supplied 

 fiom Ohio; but the greater portion of the State will soon be 

 supplied with gypsum of our own production. 



SALT. 



The manufacture of salt is rapidly assuming a great degree 

 of importance to our State. If the geological indications on 

 which I found my opinions are not fallacious, we have the most 

 magnificent saliferous basin upon the continent, east of the 

 Mississippi. As might be expected, too, the strength of the 

 brine is proportioned to the extent of the basin. 



I omit any historical notices of the rise and development of 

 this interest from the time when the State commenced legisla- 

 ting on this subject, in 1836, down to the present. Many of the 

 disappointments heretofore experienced, might have been avoid- 

 ed by an observance of such practical suggestions as are sub- 

 joined: 



1. The occurrence of a salt spring is a fact of no conse- 

 quence whatever, except in connection with all the other geo- 

 logical facts. 



2. Brine is found issuing at the outcrops of the coal measures, 

 the Gypseous Group, the Napoleon Group, the MarshalUGroup 

 and the Onondaga Salt Group. In Ohio, it also issues from the 

 Coal Conglomerate, the Hamilton Group and the Hudson Eiver 

 Group. 



3. Only two of these groups will be found, in our State, to 



