16 BULLETIN 141, U. S. DEPARTMENT OF AGRICULTURE. 



series. There are included areas of swamp and muck, which occupy 

 a small aggregate percentage of the region. The limestone rock 

 which underlies a considerable proportion of this basin also reaches 

 the surface in the form of local rock outcrop. There are a few small 

 areas where the glacial till is exposed or where it was covered to 

 such a shallow depth by the glacial lake waters that distinctive lake 

 or swamp deposits were not formed. It is probable, however, that 

 75 per cent of all of the soils found within the area of the Maumee 

 Basin have been formed, at least at the surface, through the deposi- 

 tion of lake sediments and through an unusual accumulation of 

 organic matter under succeeding swampy conditions. Frequently 

 the subsoil and deeper material consist of a gravelly glacial clay, 

 classed as till by some authorities and as glacial lake material mixed 

 with ice-borne fragments by others. 



The northern extension of the glacial lake deposits in the Maumee 

 Basin was undoubtedly connected along the southwestern shore of 

 Lake Huron with a similar area which surrounds the present Sagi- 

 naw Bay in east-central Michigan. The shore-line features are con- 

 tinuous, the sediments deposited are almost identical, and the lake 

 plain extends as a narrow border along the eastern shore of the 

 " thumb " of Michigan. 



The extensive lake plain which lies to the south and west of Sagi- 

 naw Bay was occupied by another glacial lake, which has been called 

 the glacial Lake Saginaw. It is certain that its upper stages were 

 continuous and contemporaneous with the upper stages of the glacial 

 lake waters of the Maumee Basin. 



The highest beach level formed by this lake in the Saginaw Basin 

 lies at an elevation of about 850 feet above sea level in the vicinity 

 of Flint, Mich. This is at an altitude of about 260 feet above the 

 waters of Saginaw Bay, and the present area in the Lake Sagi- 

 naw Basin thus possesses a fall of approximately 250 feet from the 

 old shore lines to the present shore line. The concentric beaches 

 around the margin of this embayment lie at several levels and are 

 usually marked by sanely and gravelly deposits, between which sandy 

 loam material prevails. The central portions of the area are some- 

 what more undulating than in the case of the Maumee Basin and con- 

 siderable areas are occupied by low morainic ridges whose crests were 

 apparently about at water level during the later stages of glacial 

 lake occupation. It appears that extensive deposits of sandy and 

 gravelly material were formed within the limits of the lake basin 

 as delta material from the streams which flowed into Lake Saginaw, 

 both from the glacial ice, forming the northeastern boundary of the 

 lake and from the exposed till upland forming its border to the 

 south and west. 



