348 PLEISTOCENE OF INDIANA AND MICHIGAN. 



tion. All the deformation found in this area seems to accord better with ice attraction than 

 with any other cause that has been suggested. 



It is therefore concluded, provisionally, that the land in the area of horizontality has in 

 fact remained practically unaffected by the great deformations which uplifted and tilted 

 the region farther north. This area appears to have remained like a steady point while the 

 region north of it was undergoing large changes of altitude and attitude. The area of hori- 

 zontality may be used, provisionally, therefore, as the measure, not merely of relative move- 

 ments, but of the absolute movements of elevation which have affected the deformed area 

 farther north since the beginning of Lakes Maumee and Chicago. But it is not certain that 

 this use has any application to times earlier than the beginning of these lakes. 



The first and second Arkona beaches show a slight convergence toward the south in the 

 northern part of the area of horizontality. In the vicinity of Birmingham the first Arkona 

 beach appears to be 6 or 7 feet above the second, and this relation continues without noticeable 

 change to the vicinity of Ypsilanti. Southward the second Arkona beach seems to rise grad- 

 ually until the interval between it and the first is only 2 or 3 feet, and it finally pinches out 

 entirely, so that in Ohio one beach appears to stand in the place of the first and second. This 

 phenomenon may be due to an entirely different cause from that which affected the Maumee 

 beaches, but it is of about the same order of magnitude. Probably it could not have been 

 caused by ice attraction alone. It appears more likely to have been due to a very gentle uplift 

 and tilting at the north following a lowering of the lake by a cutting down of the outlet. The 

 outlet being at the north, this movement may have backed the water at the south up to or 

 over the first beach. If due to deformation by some other cause these facts modify the esti- 

 mated effect of ice attraction on the Maumee beaches south of Birmingham'. 



RELATION OF MAUMEE BEACHES TO MORAINES AND OUTLETS NEAR 



IMLAY, MICH. 



So long as the Fort Wayne outlet remained continuously active the history of Lake Maumee 

 was very simple. But when the oscillating ice front had retreated as far as northeastern Lapeer 

 County, Mich., the relations began to be complicated. The first opening of an outlet near 

 Imlay probably occurred on the retreat of the ice front immediately preceding the making of the 

 Defiance moraine. Though no positive proof of such an opening is at present available, one is 

 suggested by the character of the Defiance moraine where it passes from southwestern Almont 

 Township into eastern Attica Township. It seems certain that an outlet past Imlay was opened 

 at the retreat next preceding the Birmingham moraine, the low, slender character of this moraine 

 from Romeo to Imlay being apparently due to the presence of this outlet river close along the 

 ice front. (See pp. 283-284.) 



From a point a mile or two southeast of Dryden the Defiance moraine begins to weaken and 

 from the northwest corner of Almont Township northward about 4 miles to Belle River it shows 

 the same kind of modification and weakening that characterizes the Birmingham moraine north 

 of Romeo. 



If an outlet was opened before the building of the Defiance moraine it was closed when the 

 ice readvanced to that moraine. At the next backward oscillation a new outlet was opened 

 through the same district and was in turn closed by the readvance to the Birmingham moraine. 

 Nothing definite is known concerning the first of these outlets, but in all probability the Lum 

 and Rochester channels are parts of the second one. 



At the next back step of the ice front another outlet was opened, apparently at a some- 

 what lower level, and it was during the activity of this outlet that the lowest beach of Lake Maumee 

 was made. The next step of readvance of the ice did not close the outlet but pushed it up the 

 slope to the place where the Imlay outlet channel is now found, close in front of the Imlay 

 moraine and 20 feet higher than the lowest beach. The location of the outlet channel at the time 

 of the lowest beach is not definitely known. In southeastern Lapeer County and in Genesee 

 County it appears to have been overridden and destroyed, but it was very probably followed by 

 the Imlay outlet river from near North Branch to the narrows above Columbiaville. This may 

 account for the apparent greater depth and later aggradation of this part of the Imlay channel. 



