386 E. H. Mudge — Pre- Glacial Drainage in Michigan. 



swamp, the older and higher land adjoining must natur- 

 ally have drained into it. Later, when the Huronian River 

 dissected the Carboniferous strata, the drainage from the north 

 must have gathered into a prominent stream at some point and 

 become a branch of the main river. This important branch 

 valley is, in my judgment, represented by the modern Muske- 

 gon Valley. Throughout much of the upper part of its course 

 the surface of the valley rises rapidly on either side of its 

 center, attaining an elevation of from 300 to 600 feet within a 

 limit of five or six miles on either side. The limits of the 

 valley may indeed have been determined by the presence of 

 moraines, pushed up from either side by the Saginaw and 

 Michigan glacial lobes, but much of the country is new, and 

 has never been carefully examined, and there are few borings 

 and no rock exposures on which to base an opinion. In the 

 absence of other data it may be proper to assume that the 

 drift-sheet is thinner over the more elevated portions, as in 

 the southern part of the State, in which case we can plainly 

 see in the upper Muskegon Valley a remnant of an old erosion 

 gorge. The general configuration is such as to indicate that 

 this old valley joined the main valley near Grand Rapids,* 

 though the modern river flows into Lake Michigan. 



Dr. J. W. Spencer, who has given much study to the sub- 

 ject, supposes that this region drained to the east, which is 

 undoubtedly correct. He has named the main stream across 

 the peninsula the Huronian River, and considers it as a branch 

 of his Laurentian River, which he supposes to have drained 

 the upper part of the Lake Michigan basin. But the location 

 of the two tributaries, occupying the valleys above described, 

 I think has not before been suggested by anyone. I have 

 therefore named the southern tributary the Hastings River, 

 from the chief city within the modern valley, and the northern 

 the Gypsum River, from its coincidence with the supposed 

 strike of the gypsum or sub-Carboniferous strata. The drain- 

 age system as thus made out will be clearly understood by an 

 inspection of the map. 



Ionia, Mich. 



* See the writer's paper on the " Drainage Systems of the Carboniferous 

 Area," — in American Geologist, for November, 1894. 



