GLACIAL LAKE ARKONA. 363 



submerged. This readvance divided the Arkona beaches in Michigan into four distinct areas 

 each of which has a different history: (1) The area in the Saginaw basin in which the Arkona 

 beaches were neither submerged nor modified;-*^) the area on the "thumb" in which the 

 beaches were overridden by the ice and destroyed; (3) an area in the Black River valley in 

 which the beaches were submerged but on account of their protected position were not modified; 

 and (4) the main area of Lake Whittlesey, within which the beaches were submerged and greatly 

 modified by storm waves. 



UNMODIFIED BEACHES IN SAGINAW BASIN. 



When the waters fell from the last stage of Lake Maumee and began the formation of the 

 Arkona beaches, the level at which they worked was determined by the level of the outlet then 

 established. This outlet was westward down the valleys of Maple and Grand rivers to glacial 

 Lake Chicago a few miles west of Grand Rapids. The head of this outlet is near Maple Rapids 

 in northwestern Clinton County. Here two unusually strong gravelly beach ridges, each double 

 in form, enter the valley from the east and northeast and become parallel, as shown in figure 1. 

 (See p. 258.) Their altitude is about 710 feet above sea level, and the channel between them is 

 about three-fourths of a mile wide at its head. The members of each pah are generally close 

 together, are strongly developed, and are composed of sandy gravel. Each ridge is commonly 

 75 to 200 yards wide and rises 20 to 25 feet above the flats of the former lake bottom. The 

 upper ridge is generally 5 to 10 feet above the lower one, the interval varying slightly. 



Northeast of Maple Rapids the northerly pair of beaches have a wide sweep of flat ground 

 in front of them and they grow less strong. East of Ithaca they are about a mile apart. At 

 North Star they are also faint and the descent in front of them is slight. About 5 miles south- 

 west of North Star a gravelly knoll, possibly a kame originally, stands out as an island, the only 

 one on the old shore in this basin. Where they turn westward up the valley of Pine River 

 toward Ithaca the beaches are both perceptibly weaker. Northwest from Ithaca to St. Louis 

 the upper beach is fairly strong and pursues a nearly direct course, but the lower one is gen- 

 erally faint. From Mount Forest the beaches run a little east of north through the extreme 

 northwest corner of Midland County northeastward into northern Gladwin County. In this 

 interval they grow perceptibly weaker and more broken and the lower member is difficult 

 to trace, finally being lost altogether on the sandy plain. The upper ridge is readily dis- 

 tinguished for about 7 miles northeast of Gladwin, beyond which it leaves the border of the 

 moramic ground and is not certainly traceable in the sandy plain. Its altitude 7 miles north- 

 east of Gladwin is 815 feet above sea level (aneroid). 



East of Maple Rapids the southerly pair of beaches, as shown in figure 1, diverge slightly, 

 the upper one turning south past the schoolhouse. This beach is very strong to this point but 

 grows rapidly weaker down the valley. The lower beach is not so well defined and keeps a more 

 direct course to the southwest. For 3 or 4 miles east of Maple Rapids the beaches he upon the 

 face of a bluff and are broken in many places, the lower one especially being difficult to trace. 

 At Eureka the beaches turn south for a mile and then east and are better developed. To the 

 vicinity of Elsie the beaches are both well formed as gravel ridges and are one-fourth to one- 

 half mile apart. From Elsie they run eastward past Chapin to Shiawassee River in fine form. 

 At Chapin, where they are very strongly developed and stand close together with 5 or 6 feet differ- 

 ence in height, they are composed of rather coarser gravel and contain less sand than in most 

 other localities. Eastward from a point north of Elsie the mature character of the foreslope 

 or surf-wasted zone is striking, the ground dropping 20 to 25 feet in 300 to 400 feet, from the 

 front of the lower ridge apparently to a floor that has been wasted by surf pounding for an 

 unusual length of time. This phase of shore lines is in few places so strongly developed as here, 

 though it is almost as strong at many points northeast of Clio. 



From Oakley on Shiawassee River the beaches run eastward past Lathrop Corners in strong 

 development, but after turning southeast up the Flint River valley toward Flushing they are 

 much reduced in strength. The lower beach extends nearly north from Flushing on the east 

 side of the river in fairly good development for about 2 miles, where it turns to the northeast. 



