THE GEOLOGICAL SECTION OF MICHIGAN 409 



Monroe and the Traverse (Milwaukee or Hamilton) the east or 

 Michigan side of Lake Michigan was out of water and the Wisconsin 

 post-Niagara uplift was fairly uniform from south to north. On the 

 whole, the south seems to have been first to emerge (since there is 

 more Niagara at the north and the seaward opening was to the north) . 

 •The Sahna sea was left to deposit salt. The recession or submerg- 

 ence during the Monroe may have been uniform. Whether the 

 next emergence began sooner at north or at south one cannot tell 

 since there is so decided an erosion unconformity. 



A small percentage (i to 5 per cent) of sand found in the Monroe 

 dolomites may have been wind-blown from exposed beds of sand in 

 Wisconsin. Passing northeast we find the Lower Monroe persistent. 

 I am inclined to think, therefore, that the Michigan seas of Schu- 

 chert's Upper Siluric maps should open to the north much more. 



At Port Huron the Lower Monroe is (1,215-1,555 feet) 340 feet 

 and making a considerable jump to Goderich, Canada, we find 

 between the limestone group and the salt 364 feet. This persistent 

 thickness is an argument that between Monroe County and Goodrich 

 was continuous deposition and that we have a complete section here. 

 At Grand Lake in the Alpena Land Co.'s well, we find the limestone 

 coming down somewhat farther and very thick. At Alpena the 

 whole Monroe appears to be only about 713 feet, but there are 

 discrepancies in the depth at which salt is said to occur at the different 

 wells around Alpena that may be due to dislocations of the Monroe 

 before the Traverse. 



There seems to have been a pre-Traverse dip from Alpena north, 

 enough to counterbalance the present Traverse dip the other way 

 and in that direction was limestone and the open sea. 



To the east then the submergence of the Monroe was longer, the 

 emergence at the close delayed, and as we shall see, intermittent, 

 and a land-mass formed to the south during the Upper Monroe. 



23. Sylvania sandstone. — 30 to 440 feet thick as sandstone, 170 

 feet as limestone. This, the Middle Monroe formation, is easily 

 described. It has been found only along the flank of the Cincinnati 

 anticlinal as a well-defined bed. It thins toward the outcrop where 

 it is between 50 and 100 feet thick. It is thickest in a line through 

 Milan, Ypsilanti, and Royal Oak. It probably skirts the Cincinnati 



