THE GEOLOGICAL SECTION OF MICHIGAN 401 



at Strasburg a few miles off at 534 feet only above the Trenton is 

 dolomite with a very red rock beneath it. No such rocks are clearly 

 identified in the wells in the southwest part of the state, and probably 

 were never deposited. A. simple explanation would be that there 

 was some erosion of the underlying formation here as well as along 

 the north border and that the red and the marine part of the Medina 

 was much restricted. Grabau has suggested that these red beds are 

 not marine and includes the Medina as Clinton. There seems, 

 however, to be a gradual transition from the beds below, rather than 

 sudden uplift. Moreover, why, if wholly land beds, should they be 

 restricted to the center and lower parts of the basin ? 



SILURIAN (ONTARIAN) 



Some part of the beds just described may be Ontarian, as Ulrich 

 and Cummings have said, with whose interpretation of the facts 

 Michigan stratigraphy is in entire harmony. If so they should be 

 classed as Medina, but as in many of the records of wells we have to 

 include them with the shale group below, I have preferred to associate 

 the description also. 



The term Niagaran as used in Michigan includes, in mapping, 

 Clinton to Guelph. In sections it has been used also in a slightly 

 narrower sense, not including the Clinton. 



Bigsby (1823) used the term Manitoulin limestone in an equivalent 

 sense, giving its lithological character, organic remains, and geographic 

 position clearly, but while he very clearly distinguished it from the 

 St. Joseph (= Trenton limestone) and the Mackinaw (Dundee- 

 Monroe =Helderberg in its original broad sense) limestones, he did 

 not separate it from the shaly beds immediately above and below, 

 which are indeed far from conspicuous in the outcrop. If we use the 

 term Manitoulin, these limits may then be set to suit our convenience 

 so long as the local equivalents of the Guelph and Lockport are not 

 excluded. 



As the Trenton marks the first, so the main mass of the Niagara 

 (Schuchert's Louisville) marks the second. Paleozoic period of 

 "epicontinental seas" of large transgression over the continent. 

 The fact that Niagara is found in Limestone Mountain on Keweenaw 

 Point, near Hazel Station of the Mineral Range Railroad, makes it 



