4o8 A. C. LANE 



as Kraus has shown for Monroe County, probably filled by (strontium 

 sulphate) celestite, are characteristic rocks both in Monroe County 

 and in the Upper Peninsula. A series of wells at intervals of but a 

 few miles at most have penetrated this series from the Ohio line to 

 Port Huron. It outcrops and is exposed again near St. Ignace and 

 Mackinaw City and the islands north of Beaver Island. It probably 

 touches the Wisconsin shore near Milwaukee, and is reached by a 

 series of deeper wells along the western side of the state. A list of 

 locations will be found in the report for 1908. 



As the total thickness from the base of the Sylvania down to the 

 salt shown in numerous sections runs only from 337 to 400 feet at the 

 outside, Grabau's estimates of the thickness of the subdivisions 

 cannot be added. It is very often impossible to make lithological 

 subdivisions. A bed of sandrock often occurs under the main 

 Sylvania sandrock a short way. The Waubakee dolomite fossils in 

 Wisconsin most suggest the list of the Raisin River and Put-in-Bay 

 beds, and I think there is reason to believe this series more widespread 

 and persistent than the series above or below. The salt series below 

 certainly does not extend so far either to the south or to the north. 

 To the southeast down in Ohio, where the Sylvania sandstone is very 

 thin and the overlying beds between that and the Devonian limestones 

 easily overlooked, this lower Monroe is still persistent. The fossils 

 reported from Milwaukee and from the Upper Peninsula by Romin- 

 ger' are Lower Monroe rather than Upper Monroe forms. 



Finally as we trace the beds from the thinner "Helderberg" or 

 Monroe sections of Indiana toward the thicker sections, between 

 Algonac and Alpena, the addition seems to be of beds above and 

 below to a nucleus of Lower Monroe which remains fairly uniform 

 in thickness. But there is this difference as we trace the section 

 north along the Lake Michigan shore from that which happens as 

 we go east toward the Cincinnati anticlinal. In the former case the 

 Traverse (Hamilton) thickens, but very little is seen of the Dundee 

 beneath — between it and the Monroe — in fact, there does not appear 

 to be much added to the Monroe itself. The explanation would seem 

 to be that for a good part of the marked erosion intervals (Waubakee 

 or Helderberg) between Niagara and Monroe and again between the 



I Michigan Geol. Surv., I and III, 28. 



