E. H. Mudge — Pre- Glacial Drainage in Michigan, 385 



In the same manner two other lesser ancient valleys may be 

 postulated with some confidence. The first of these is repre- 

 sented by the valley of the Thornapple river, which enters the 

 Grand a few miles east of the city of Grand Rapids. The 

 depression occupied by this stream and its branches is rather 

 broad and flat, and within its area there is a large number of 

 small lakes. It is therefore not a product of post-glacial ero- 

 sion. Borings at Hastings and at other points near the river 

 passed through more than 100 feet of drift without finding 

 rock. That this valley is also a remnant of an older one is a 

 legitimate inference. 



(l fRIf) 



The second ancient valley referred to is buried beneath the 

 valley of the modern Muskegon River. This stream rises in 

 the highlands of the north central part of the peninsula, and 

 flows directly southwest, reaching Lake Michigan only a few 

 miles north of the mouth of Grand River. Its drainage area 

 is peculiar, having a length of about 125 miles, while its lateral 

 extent averages about 25 miles, and at some points is much 

 narrower. That this elongated area is the modern representa- 

 tive of a pre-glacial valley is not claimed with so great confi- 

 dence as in the case just described, though there is good reason 

 for accepting this hypothesis. It will be noted, in the first 

 place, that there is a large area, tapped by this supposed valley, 

 which must have had a drainage system of some sort. When 

 the central part of the peninsula was a great Carboniferous 



