430 



PLEISTOCENE OF INDIANA AND MICHIGAN. 



localities and into the second series in others. On this account some of his measurements on 

 the lower members of the series are used with a reservation of doubt as to the accuracy of the 

 identification. 



In 1912 Mr. Leverett made wye-level surveys of the Algonquin and lower beaches on St. 

 Josephs Island, Ontario, and along several hnes in the northern peninsula of Michigan. 



Deformation of the upper Algonquin beaches.- — Spencer's surveys and Goldthwait's later 

 work have put the discussion of the deformation of the beaches upon a much better basis than 

 formerly. Though more detailed work might seem desirable, the increased expense wordd hardly 

 be justified for the whole field in the present stage of investigations. In all probability the 

 need of more detailed work in certain limited critical areas will be brought out more clearly 

 by these and other similar surveys in the near future. 



Besides a higher degree of accuracy in general for determinations of altitude, Goldthwait's 

 work has afforded a stronger, safer basis for the identification of individual beaches or water 

 planes from place to place and has led to an important modification of views formerly held as to 

 the relations of the weaker beaches which lie in the interval between the Algonquin and the 

 Nipissing. At Mackinac Island the vertical interval between these two principal shore lines is 

 about ISO feet. But it narrows southward to only 10 feet in the area of horizontality. It was 

 formerly thought by some investigators, including Mr. Leverett and the writer, that the Battle- 

 field and Fort Brady beaches, which are displayed in this interval in the north, were related to 

 an eastward outlet to the Ottawa Valley and hence did not converge to the same hinge line as 

 the Algonquin. But though Goldthwait did not trace these beaches down to the hinge line, he 

 traced the Battlefield beach far enough to show clearly that its plane converges with the upper 

 Algonquin beaches toward the hinge line. The proofs are not so clear for the Fort Brady beaches, 

 but the facts in hand seem to indicate that they converge to the same line. 



The members of the upper group of the Algonquin beaches also converge southward toward 

 the hinge line. The altitudes of the highest Algonquin, where determined by wye-level measure- 

 ments on the east side of Lake Michigan, are given below. The first three measurements are 

 at localities farther north and are introduced to show the continuation of the tilted plane. 

 (See PI. XXIII.) The altitude of Lakes Huron and Michigan is taken to be 581 feet above sea 

 level in all the following tables : 



Wye-level altitudes of highest Algonquin beach on the east side of Lake Michigan. 11 



Sault Ste. Marie, Ontario, 6 miles north 1,015 434 Lawson. 



Rexford, Mich. (probably highest) &930 349 Leverett. 



Hessel 863 2S2 Goldthwait. 



Mackinac Island c 



Cross Village 



Beaver Island 



Harbor Springs 



Norwood 



Northport 



North Manitou Island 



Traverse City 



Frankfort d 



Herring Lake 



Arcadia 



Muskegon 



Spring Lake 



Holland 



1 1n his early work the writer made many measurements of altitude on the Algonquin and Nipissing beaches by aneroid barometer and 

 hand level, but these are now nearly all superseded by more accurate measurements by others. 



t> Railroad. 



c On Mackinac Island the altitude given by Goldthwait (812 feet) is for a small, flat bench of gravel nearly 3 feet higher than the strong highest 

 beach. The little bench is not the same kind of feature as the strong beach ridge. It gives no evidence ofhaving been made by wave action and 

 is therefore hardly to be put into the same category as the strong beach ridge. If it marks t lie level of the higher water body it must have been of 

 local extent and without waves of any importance. If it is due to ice jamming during Lake Algonquin it is not a wave-made feature. In any 

 event, it seems best not to take it as a point in the Algonquin plane in discussing the deformation of that plane. Goldthwait's measurement of 

 the highest beach is about son feet and that value is used here. 



i It is almost certain that the altitude given for Frankfort is not a record of the highest Algonquin. At Onekama on Portage Lake and at Bar 

 Lake 4 miles north of Manistee the highest beach recorded is about 16 feet above the lake if.'.iT feet altitude). This apparently is the Nipissing 

 beach. The absence of the Algonquin beach seems to be due to the. fact that during the time of that lake the enibavmenls of Portage and Bar 

 lakes were shut off from the main lake as Portage and Muskegon lakes are to-day, so that the surf did not come into them from the large lake. 

 Later, during the Nipissing Ureal Lakes, the obstruction was cut awav and the waves entered and made a record of that lake level at the head of 

 the embayments. At Frankfort the highest record is probably that of one of the lower members of the upper Algonquin group rather than of 

 the highest. 



