276 PLEISTOCENE OP INDIANA. AND MICHIGAN. 



before, and the channel continues thence to a point 2 or 3 miles southeast of North Branch with 

 a width of one- third to one-half mile between high, steep bluffs. 



The lands bordering the Imlay channel from Almont to Imlay are relatively low on both 

 sides; except for a large knoll running a mile northeast from Almont on the west side and a 

 narrow morainic ridge east of Imlay they nowhere exceed 30 or 40 feet. From Imlay to Mill 

 Creek the banks on the east side continue with the same low relief , but from Mill Creek to the 

 transverse channel south of North Branch the moraine presses up to the east side of the channel 

 and for 8 miles forms a steep bank 70 to 80 feet high. In this interval the channel is floored at 

 many places with gravel and sand and at some places contains small bars or terraces. The peat 

 on the northern divide is not deeper than 3 feet. On the west side a high, rugged moraine forms 

 a steep bank to the channel through the whole interval to North Branch. The kames described 

 above form the highest points. 



From the point where the transverse channel enters the Imlay outlet above North Branch 

 the channel floor becomes wider and the banks somewhat lower. The floor is swampy to a point 

 below North Branch, but through the southern part of Rich Township the banks are lower and 

 the floor is bowldery. On leaving Rich Township the channel turns southwest and keeps this 

 course to the 'county line. Except for about U miles above Columbiaville, the channel in this 

 interval is a full mile in width and is floored with sandy gravel. The gravel filling begins near 

 the north line of Deerfield Township, reaching some distance eastward into the mouth of the 

 Lum channel and expanding to a width of more than 2 miles just above the narrows northeast of 

 Columbiaville. In the narrows there is not much gravel, but below Columbiaville the channel 

 widens again to a mile, and the gravel extends to the county line and also some distance up the 

 Elba channel. From Rich Township to the narrows the bed of the modern Flint River is 

 trenched into the gravels about 10 feet, Below Columbiaville the gravels stand as terraces 20 

 to 25 feet above the river. A mile or two south of the town the terrace on the east side carries 

 a number of basins. The heavy gravel terraces continue to Flint and Flushing. 



The origin of the narrows above Columbiaville is not clear. The Imlay channel when first 

 made probably had the average width in this interval, and the expanded portion just above 

 the narrows suggests an obstruction introduced after the first cutting of the channel, probably 

 by a readvance of the ice. As just stated, the wide part above the narrows may be a part 

 of the Lum channel. There are several good-sized kames at the head of the narrows on the 

 south side. It seems probable that some of the marked irregularities of the morainic ridges 

 west and north of Columbiaville are due to readvances of the ice into the westward extension of 

 the Lum channel and that the channel was overridden and obliterated by these readvances. 



Between Almont and North Branch there are three low divides in the channel. One is 1£ 

 miles north of Almont, another 3 miles north of Imlay, and the third 2 miles south of the 

 Deanville kames. All are flat and are covered with peat and would not be noticeable, except 

 that they divide the water in the channel and turn it into different drainage systems. 



Gradient. — In order to get an adequate conception of the relation of the Imlay outlet channel 

 to Lake Maumee it is necessary to consider to what extent the northward differential uplift has 

 affected the channel since it was made. In the Ann Arbor quadrangle the highest Maumee beach 

 has an altitude of 800 feet and was affected very little if any by differential uplift. But 4 or 5 

 miles north of Birmingham it begins to rise northward, and from the vicinity of Rochester it 

 rises at an average rate of about a foot in a mile. This brings the beach at Almont to an 

 altitude of 840 feet and at Imlay of about S50 feet. At Almont, therefore, the beach is 

 40 feet higher than it is at Birmingham, where it was not uplifted. 



The floor of the Imlay channel H miles east of Almont has an altitude of 796 feet. But 

 since this is 40 feet higher than it was formerly, its altitude before deformation was about 756 

 feet. East of Imlay the channel floor is about 800 to 802 feet 1 and on the divide south of the 

 Deanville kames it is about the same. At Imlay its altitude was formerly 50 feet lower than 



i The altitude of the Huckleberry Marsh in the Imlay channel 3 miles north of Imlay is SOS feet as determined by Mr. Leverett by wye level 

 from Imlay, but a pole can be run down there 10 feet or more in slush, so that the outlet floor is below S00 feet. 



