GLACIAL LAKE ALGONQUIN. 419 



level. The dunes associated with this beach appear not to have been blown up from the present 

 shore, but to be as old as the Nipissing beach, some possibly as old as the later lower stages of the 

 Algonquin. 



Southwest from Sebawaing the split-up ridges of the Algonquin spread more widely after 

 passing about 5 miles into Tuscola County and entering the extensive swamps east and south 

 of Quanicassee. 1 They become weaker and more fragmentary on account of the very wide 

 flats in front of them and seem to be composed of sand without gravel. Some contain a consider- 

 able amount of clay and are suspected of being in part ramparts like those associated with the 

 Maumee beaches in Ohio. (See p. 337.) The faint upper ridges reach south into the southeast 

 corner of Saginaw County and a few weak bars extend northwest past Munger to Bay City, but 

 most of these fragments are not up to the level of the upper strand of the Algonquin. The divide 

 between Saginaw Bay on the north and Saginaw and Cass rivers on the south is a low, broad 

 ridge of clay — a water-laid moraine — of which the lower parts are distinctly below the Algonquin 

 level. South of this ridge a sprawling, irregular-shaped basin covering the lower reaches of 

 Cass, Flint, Shiawassee, and Tittabawassee rivers was evidently a shallow bay of Lake Algon- 

 quin. Unless some sandy ridges near St. Charles belong to it, no distinct beach has been found 

 at the Algonquin level in this basin, though sandy areas associated with the rivers where they 

 enter the Algonquin level seem to suggest the margin of a lake which reached up the valley of 

 the Tittabawassee to Sanford, about 25 miles above the head of the Saginaw, and 8 to 10 miles 

 up each of the other rivers. 



Bay City to Au Sable River. — From the wide flats along Saginaw River south of Bay City 

 a shallow and very irregular shaped depression runs northward behind or west of the main 

 Algonquin ridge, which runs north-northwest from Bay City. It is probable that a sandy belt 

 along the west bank of the broader part of this depression, passing through southern Monitor 

 and central Frankenlust townships was made by the early waves of Lake Algonquin before 

 the barrier ridge northwest of Bay City was built. It lies at about the altitude of the upper 

 Algonquin. 



A rather light, gravelly beach ridge in the cemetery in the southeast part of Bay City is 

 apparently slightly below the upper level of Lake Algonquin. But on the west side of the river 

 the main ridge begins again, curving from north to northwest to Kawkawlin, thence curving 

 gradually north and slightly east of north to Pinconmng. The beach here is a heavy barrier, 

 composed mainly of fine sand, rarely with gravel and pebbles, lying 1 J to 2 miles back from the 

 present shore, except back of Lengsville, where it is little more than a mile. Toward Pin- 

 conning and beyond, the beach is broken at shorter intervals but continues as a strong sandy 

 and in places gravelly ridge with much sand in front of it and behind it. A few small dunes 

 lie along the line of the main ridge. 



In Arenac County the main ridge passes half a mile west of Saganing and just west of Pine 

 River, curves a little east, and passes about 1£ miles southeast of Omer. For 2 or 3 miles north- 

 east of Arenac, however, it is modified by the contemporary delta of Rifle River which spreads 

 a mile or two on either side. From Arenac northeast and east the beach is considerably farther 

 inland and more fragmentary. For 2 to 4 miles east of Omer it is a heavy gravel ridge. East- 

 ward across Au Gres River only detached and rather weak fragments of the upper strand were 

 found. West of Whitestone Point a well-developed continuous gravel ridge runs about a mil e 

 back from the lake northward to Alabaster, in Iosco County. Just south of Alabaster the 

 Algonquin beach comes close to the present lake shore, mainly as a gravel ridge but at two 

 or three places as a cut with a low cliff. 



From Alabaster northward to about 1| miles northwest of Tawas the Algonquin beach has 

 been completely cut away, not by the present lake but by the Nipissing waves. The Nipissing 

 and modern beaches combined form a flat about a quarter of a mile wide and the cliff increases in 

 height from zero at Alabaster to about 70 feet and is very steep. The highest part is about 1 \ 

 miles north of Alabaster and extends north for about a mile. It is composed mainly of till, with 

 some sand and gravel on top. Bedrock outcrops on the shore at Alabaster. 



1 Davis, C. A., Report on geology of Tuscola County: Michigan Geol. Survey, 1908, map of surface geology. 



