744 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



about 70 feet from the col east of Ubly to Cass City, about 22 miles, but the descent 

 of the water surface was probably somewhat less. 



Cass City is built upon a gravel plain about 2 miles long east and west and 

 nearly a mile wide, which from its position strongly suggests that it may be a delta 

 of the outlet of Lake Whittlesey. Its top level is about 750 feet above sea level or 

 20 to 26 feet above the old channel bottom. There appeared to be a fragment of the 

 same plain on the south side of the river also, as though the original deposit had been 

 cut in two. 



The contemporarj^ position of the ice front with respect to this outlet is very 

 clearly marked. The last land-laid moraine of the Huron lobe of the ice sheet lies 

 close to the east side of Black River all the way northward from a point 6 or 8 miles 

 northwest of Port Huron. Where the Black River Swamp is wide the main crest of 

 the moraine is sometimes i or 5 miles from the river, but it is usualty half that 

 distance or less. The moraine is usually dual or triple in form, with 2 or 3 crests 

 (XV ridges running roughl}' parallel half a mile to a mile and a half apart, the western 

 one being the highest. Toward Ubly the moraine trends northwest, and at a point 

 about 3 miles northeast of Ubly it meets the contemporary moraine of the Saginaw 

 lobe coming from the southwest, and the two form a sharpl}^ defined angle of 75^. 

 The high ridges of the two moraines do not unite, but are cleft just in the angle. A 

 small brook, the headwaters of Willow River, drains a part of the gravellj^ channel 

 bed at the extreme north angle of the bend and carries its waters awa}^ north through 

 the narrow gap to Lake Huron, near Grindstone CAty. This cleft probably marks the 

 entrance of a small glacial tributarj^ to the great outlet river flowing from the ice 

 sheet when its front rested close bj^ on the main moraine. The bend of the channel 

 is exactly in the angle of the two moraines, but the narrowest point is half a mile 

 farther west. The crest of the Saginaw moraine from the bend to Cass City is 80 to 

 100 feet or more above the channel floor, and the channel runs close along its foot all 

 the way. The inner angle of the bend is held bjr a high, steep hill of drift, with manj^ 

 bowlders. It is the northwest end of a lower ridge, which seems to belong to the 

 eastern or Huron lobe of the ice sheet. This hill has been cut away to some extent 

 on its north and west- sides, leaving many bowlders at its base. The base of the 

 moraine opposite is also quite steep, apparentlj' from the same cause. The hill in 

 the angle evident^ once extended a little farther to the northwest. Southwest of 

 Tyre morainic ridges, mostlj' of moderate height, trend in a general east-to-west 

 course. One of these Ij'ing next south of the Tyre branch is high at its west end, 

 like the one north of Ubl}^, and appears at one time to have stood in much the same 

 relation to the river. It stands in the angle where the Tyre channel turns southwest 

 into the main channel. 



The Tyre Ijranch was apparently opened before the Ubly, and the former served 

 as an outlet, while the ice front of the Huron lobe still rested on the morainic ridge 

 which now separates the two branches. A later retreat of a mile or two bj^ this lobe 

 left an open space close along the ice front in the new position, and this became the 

 Ubly branch. After the Ubly branch opened the volume of discharge by the Tyre 

 channel must have been largelj' decreased, but the level of the lake was probablj^ not 

 lowered much, for the heads of both branches are nearlj^ at the same level. Judgino- 

 from the comparative magnitude of the moraine between the channels and the later 



