THE GEOLOGICAL SECTION OF MICHIGAN 407 



As shown by various records, the Cincinnati anticHnal had formed 

 and was out of water and divided the Salina sea' into two basins, 

 connected perhaps by a channel through Canada between Goderich 

 and Petrolia, north of Wallaceburg and Port Rowan, the one the New 

 York basin, the other the Michigan. 



The earher salt beds appear to be heavier. A great many records 

 report salt coming directly on top of "lime." Now this does not 

 mean much, for without samples and careful observation one cannot 

 discriminate limestone, dolomite, and anhydrite (anhydrous sulphate 

 of lime). In many cases where samples have been saved, under the 

 salt comes anhydrite and a good part of that which is reported as lime 

 is really anhydrite. But in some it appears as if salt really did lie 

 directly on dolomite. An explanation is suggested in my report for 

 1908, dependent on a supply of alkali water replacing the base cal- 

 cium by sodium, making sodium chloride more likely to precipitate 

 but retarding precipitation of calcium sulphate. 



22. Lower Monroe. Bass Islands Series. 365-500 feet. — This 

 is a series of dolomites with beds of oolite like those around Great 

 Salt Lake, as Sherzer has shown. The cessation of salt-making 

 may simply show that the climate had so changed that there was 

 enough of a supply of water to keep the more soluble chlorides from 

 forming. Or there may have been some light crustal shifting opening 

 an outlet. There is in Michigan no sign of structural break ^between 

 this and the Salina. 



Grabau subdivided as follows, provisionally:^ 



d. Raisin River dolomite, zone of Whitfieldella prosseri with oolite zones 200 ft. 



c. Put-in-Bay dolomite, zone of Goniophora dubia; Leperditia also. . . . 100 ft.-f- 



h. Tymochtee beds ? (Winchell Ohio) 100 ft. ± 



Relations unknown; quite likely equivalent to some other division, 



shaly and thin-bedded 



a. Greenfield dolomites, Northern Ohio 100 ft.± 



The fullest lithological descriptions are given in the Monroe 

 County report by Sherzer, VII, 46-100. Fossil lists are given by 

 Grabau, Bull. G.S.A., XIX, 545-49. 



Oolite and sandy dolomites and dolomites with anhydrite which 

 is primary, acicular or gashed dolomites in which the hollows were, 



1 Schuchert, PI. 70, somewhat modified. 



2 Bidl. G.S.A., XIX, 554. 



