GEOLOGICAL EXPLORATIONS IN MICHIGAN 



By ERWIN R. POHL, 

 Aid, Division of Stratii/raphic Paleontology, U. S. National Museum 



Under an arrangement existing between the LI. S. National AIu- 

 seum and the Milwaukee Public Museum an expedition, represented 

 by myself for the Museum and by Mr. Gilbert Raasch, Assistant 

 Curator of Geology of the Milwaukee Museum, was formed with the 

 purpose of continuing the detailed study of the little-known but 

 highly important stratigraphy of the Middle Paleozoic of the mid- 

 eastern and central Llnited States. In the two previous years the 

 work had been carried as far west as the Ontario peninsula. In pur- 

 suance of the general outline this year's itinerary took us through 

 the northern central basin province. 



The collections of the National Museum already contained much 

 excellent material from many of the IMichigan localities ; but the 

 disconnected data, brought together over a period of a half century 

 by a score of collectors interested primarily in the quality of their 

 specimens, was insufficient to a clear understanding of the geologic 

 history of the region. It was hoped that the results of this explora- 

 tive work would not only throw light on the gaps in the sequence 

 but also establish tie-points with beds of similar age in neighboring 

 areas. 



The area covered by eastern Wisconsin, southern peninsular Michi- 

 gan, and southwestern Ontario is in the region of the ground moraine 

 of the Great Glacier. Most of the topographic features of this coun- 

 try are thus due to glacial phenomena and only in certain portions of 

 it is the bed-rock exposed. Such patches, due to subsequent denuda- 

 tion, are to be seen in the vicinity of INIilwaukee, in a narrow band 

 near the northern edge of southern Michigan, and near the shores 

 of Lake Huron in Ontario. From the fossils contained in the out- 

 crops of these beds it has long been known that the period of deposi- 

 tion was during Middle Devonian times ; but the actual interrelations 

 among themselves and their positions in the type section of this age, 

 as it is evidenced in New York State, has formerly remained unde- 

 termined. 



