MICHIGAN ACADEMY OF SCIENCE. 35 



Arkona beaches extend nearly to Cass City as gravel ridges almost as strong as they are 

 farther west where they would be much more exposed. Towards Cass City these ridges 

 become Ijuried under sandy delta deposits near the mouth of the Ubly outlet ciiannel. 

 The situation is somewhat like that in Black River valley. With the Port Huron moraine 

 where it is now these beaches could not have attained such strength as they show near 

 Cass City. They were made before the moraine was built, and this moraine is the same 

 one that stands in front of the Arkona beaches in the Black River valley. 



(4) From their strength near Applegate and Cass City it seems certain that the Arkona 

 ridges once extended northward around the thumb, crossing its crest a little south of Bad 

 Axe. Between Cass City and Applegate, therefore, the Arkona ridges appear to have been 

 overridden and destroyed by the ice when it re-advanced to the place of the Port Huron 

 moraine. It is plain that the same re-advance that raised the waters on the east side of 

 the thumb to the Belmore level would have no effect on the level of the water on the west 

 or Saginaw side, because the outlet for the lake in the Saginaw valley was westward through 

 the Grand River channel and the re-advance of the ice did not touch this channel or even 

 come near to it. 



lu southeastern Michigan the Arkona beaches may therefore be divided 

 with respect to their history into four provinces or areas. First, in the 

 Saginaw valley they have not been modified in any wa}', either by over- 

 riding or submergence ; second, on the thumb between Cass City and 

 Applegate they have been overridden and destroyed; third, in the Black 

 Eiver valley they were submerged, but were, at the same time, so pro- 

 tected as to be preserved without suffering discoverable modification, and 

 fourth, in the interval from Spring Hill southwest to the Ohio line they 

 were submerged and greatly modified, their relief being much reduced — 

 in some parts destroyed — and their composition changed by the infil- 

 tration of clay. 



Evidences shoAving slight movements of re-advance on the part of the 

 ice front were found in a number of places some years ago. But, with 

 perhaps one exception, they show nothing definite as to the amount of 

 re-advance. The relations on the thumb seem to show very clearly a re- 

 advance of at least fifteen to twenty miles. 



In that case, the re-entrant angle between the Huron and Saginaw 

 ice lobes during the time of Lake Arkona was somewhere near Port 

 Austin on the end of the thumb. This would leave a strait across the 

 outer part of the thumb at the Arkona level connecting the waters on 

 the two sides. In its re-ad\'ance the re-entrant angle of the ice pushed up 

 the slope of the thumb to Ubly which is about two hundred feet higher 

 than Port Austin. In the last part of its re-advance the ice carried the 

 water level on the east side of the thumb up with it from the lowest 

 Arkona beach to the Belmore beach, but did not effect the level of the 

 waters in the Saginaw valley. Thus, Lake Whittlesey was an incident 

 of a glacial re-advance following a movement of retreat during which 

 Lake Arkona had its entire period of existence and made all of the Ar- 

 kona beaches. Besides showing that there was a re-advance of fifteen 

 to twenty miles, the Arkona beaches show that the time during which 

 the ice front rested after its retreat and before its re-advance to the 

 Port Huron moraine was fully as long as the time during which it 

 rested on that moraine. While the ice front was resting near Port 

 Austin before its re-advance it must have been building a moraine com- 

 parable to the Port Huron moraine. But this was probably overridden 

 and destroyed during the re-advance. This overridden moraine was be- 

 ing built while the Arkona beaches were being made, and the time which 

 they required for their making was time enough for the building of that 



