228 PLEISTOCENE OF INDIANA AND MICHIGAN. 



'The discharge from Grand Rapids southward to Rabbit River probably continued until 

 the ice border had withdrawn to the vicinity of Jamestown, when a passage was opened past 

 that village into the lake on the lower Kalamazoo. Aneroid readings indicate that the alti- 

 tude of the Jamestown channel was very nearly the same as that of the Ross channel, each 

 being apparently between 680 and 700 feet at the present water partings in these channels. 

 The Jamestown channel is very much smaller than the Ross channel, being about one-eighth 

 mile wide, whereas the Ross channel is about one-half mile. It may, therefore, have carried 

 'only a portion of the glacial drainage, in which case the Ross channel continued in operation 

 until a lower outlet farther west became available. 



A small glacial lake seems to have been present southeast of Holland at an altitude higher 

 than either the Ross or the Jamestown channel. The lake stood between the large morainic 

 ridge north of Rabbit River and the smaller ridge immediately south and east of Holland. The 

 southern shore of the lake is marked by a definite sandy ridge that passes through Fillmore 

 and Overisel along the inner slope of the morainic ridge. Its altitude is about 120 feet above 

 Lake Michigan, or 700 feet above sea level. The sand ridge corresponds pretty closely in 

 altitude to a narrow sag or depression east of Drenth, which leads across the divide between 

 Black River and Bear Creek and which seems likely to have served as an outlet for this small 

 lake into the Bear Creek valley and thence, by a descent of about 20 feet, to the lake on the 

 lower Kalamazoo. The sand ridge on the border of this small lake was mentioned in Mono- 

 graph XXXVIII as a possible high shore of Lake Chicago, but further studies in that region 

 have led to the abandonment of this interpretation. 



North of Grand River in eastern Ottawa County narrow sags between the morainic ridges 

 are filled to some extent by sand and gravel that was probably deposited in part as outwash 

 during the development of the morainic ridges and in part as glacial drainage from districts 

 to the north. The sandy strip east of the eastern of the two till ridges in the region heads 

 in the valley of East Crockery Creek, but leaves that valley near Conklin and passes to the Sand 

 Creek valley, through which it continues to the Grand River valley. Its altitude at Conklin 

 is very nearly 700 feet, or sufficiently high to have thrown the discharge past either Ross or 

 Jamestown, in case no lower passage toward the west was available. 



The sag between the two till ridges of northeastern Ottawa County appears to have been 

 utilized by the glacial drainage from West Crockery Creek, the glacial stream having left the 

 Crockery Creek valley near the Muskegon-Ottawa county line. It was probably also utilized 

 by the drainage from a small glacial lake that occupied a sand plain on the borders of the Mus- 

 kegon Valley, a few miles east of Muskegon, there being a swampy channel just north of Ravenna 

 that afforded a passage from this sandy plain into the Crockery Creek drainage. This swampy 

 channel is at about the level of the flat sandy tracts, or very nearly 690 feet above sea level, 

 as indicated by railway stations at Mooreland and Twin Lakes. 



It is probable that an outlet directly into Lake Michigan near Holland had been opened 

 by the time the westernmost till ridge in Ottawa County was formed. The altitude of the waters 

 on the east side of the till ridge would be likely to be governed by the height of the ground 

 (about 680 feet) on the east side of the western till ridge immediately north of Zeeland. 



REENTRANT DISTRICT BETWEEN THE SAGINAW AND LAKE MICHIGAN LOBES. 



By Frank Leverett. 



In the discussion of the Kalamazoo and Valparaiso morainic systems of the Lake Michigan 

 lobe the interlobate moraine between the Lake Michigan and Saginaw lobes was shown to 

 extend northward to Cadillac. The present discussion aims to bring out the leading features 

 in the reentrant district from the vicinity of Cadillac northward and eastward to the valleys 

 of Manistee and Au Sable rivers. In this reentrant district the recession of the ice border, 

 which was more pronounced than in neighboring parts of either of the lobes, formed several 

 ridges and groups of knolls, which will be considered in order from older to younger. 



