CUMBER SPILLWAY. 43 



two from Ubly, and the outlet river from the col to Cass City flowed close 

 along the foot of the ice-front. This position of the outlet was a natural 

 consequence of the fact that that ice-front was retreating northward down 

 a slope which happened to be the lowest part of the rim of the lake. For 

 this reason the outlet hugged the receding ice-front and changed its place 

 as fast as lower points of escape were uncovered. 



By following the course of the Saginaw moraine to the southwest, 

 curving back to the north on the west side of the valley, and the course 

 of the Port Huron moraine to the southeast, curving back to the north- 

 east in Ontario, we find the exact position of the great ice-dam in the 

 basins of Saginaw bay and the south arm of lake Huron. It only re- 

 mains to locate the contemporary ice-front in the eastern part of the 

 Erie basin to know the exact boundaries of lake Whittlesey. 



C UMBER SPILL WA Y. 



South of the Tyre branch and the united channels below and separated 

 from them by a morainic ridge only a mile to two miles wide is an open 

 valley which passes about a mile north of the villages of Freiburger, 

 Cumber, and Wickware. The lower part of it near Cass City is a swamp, 

 which we may call the Stone Wall swamp. This swamp is several miles 

 long and in many ways resembles the greater outlets here described, but 

 is somewhat narrower. It looked at first like an old outlet that might 

 have had an importance in the lake history comparable with that of the 

 T}^re-Ubly channel, and it was so regarded until the upper part was seen 

 later. It was found in the end, however, to be another channel, with 

 much the same history as the early history of the Tyre branch channel 

 described above ; that is, it was a spillway open only a short time during 

 an active period of glacial recession, and soon abandoned for the newly 

 opened Tyre and Ubly channels. The first activity of the Tyre branch 

 itself was probably as a spillway, its function as part of the more perma- 

 nent outlet beginning only when the Ubly channel had opened also. 



The Cumber spillway lies close to the Tyre-Ubly channel on its south 

 side throughout its whole length, and extends past Cass City about four 

 miles on the southeast and appears to fade away on the plain north of 

 Deford. The south branch of Cass river crosses it southeast of Cass Citv. 

 Its altitude at its mouth is about the same as that of the Tyre-Ubly 

 channel. The morainic ridge between the Cumber and Tyre-Ubly chan- 

 nels is 40 to 70 feet high, but at one point half way down the channel 

 this ridge is broken, and through this break a creek drains the upper 

 part of the spillway channel into Cass river at Holbrook. 



The lower part, four miles east of Cass City, is a wet peat bog a little 

 less than half a mile wide, with marl beneath. Extending for a consid- 



