158 Madge — Notes on Preglacial Drainage in Michigan. 



Art. XVII. — Farther Notes on Preglacial Drainage in 

 Michigan ; by E. H. Mudge. 



The most complete study and discussion of the surface geol- 

 ogy of Michigan that has recently been published is contained 

 in No. 30 of the Water Supply and Irrigation Papers of the 

 IT. S. Geological Survey, under the title, " Water Resources of 

 the Lower Peninsula of Michigan," by Alfred C. Lane, State 

 geologist. Besides much information of economical impor- 

 tance, this pamphlet contains a series of very useful maps, an 

 attempt to work out more fully than has heretofore been 

 done the system of Preglacial drainage, and other matters of 

 more special scientific interest. Prof. Lane has probably given 

 more study to the records of deep wells and other similar data 

 than any other man in the state, and concludes that the theory 

 of Dr. Spencer, heretofore adopted by the writer, that in Pre- 

 glacial times a large stream flowed across the state from west 

 to east at about the locality of the Grand-Saginaw valley, is 

 incorrect. He believes that the principal Preglacial stream had 

 its rise in the vicinity of Saginaw bay, flowing west and north- 

 west across the peninsula to the vicinity of Manistee, on the 

 Lake Michigan shore, a route far to the north of the Grand- 

 Saginaw valley. 



This conclusion is based, first, on the fact that a limestone 

 ridge is believed to extend clear across Saginaw bay at a level 

 so high as to render a large drainage channel in that direction 

 extremely improbable ; second, on the condition of the rock 

 surface in the vicinity of Manistee, which so far as known is 

 extremely broken and uneven, characteristic of a locality well 

 down the course of a stream rather than near its head ; and 

 third, deep borings at scattered intervals along the line find 

 the rock-surface at lower levels than is known elsewhere in the 

 state. 



The writer has no preconceived theories which he is bound 

 to maintain, and concedes that Prof. Lane's theoiw rests on 

 coherent even if somewhat meager evidences. However, the 

 element of speculation is necessarily large, and the problem 

 can scarcely yet be considered definitely settled. I desire to 

 present some new facts bearing on the question, which render 

 it necessary to modify quite materially Prof. Lane's contour 

 map of the rock surface (Plate VI of his pamphlet). As a 

 matter of course, in the present state of knowledge, large 

 areas of the rock surface being totally unknown, such a map 

 must contain a large element of guesswork, and Prof. Lane, I 

 am sure, will welcome any corrections of the same. His map 



