320 LIFE OF THE PLEISTOCENE 



who will take the trouble to study and classify the material in these buried 

 forests. There should also be found with the vegetation a varied fauna of 

 mollusks and insects, as well as vertebrates. 



6. MINNESOTA 



Upham has recognized the Sangamon interval in Minnesota, tho no evi- 

 dences of life are mentioned. The location of this stage is thus described. 164 

 "Three chains of lakes on the till area of Martin County, one of the central 

 counties of the southern tier in Minnesota, adjoining Iowa, are ascribed to inter- 

 glacial erosion of rivers flowing south, where now the courses of drainage pass 

 eastward. The duration of this interglacial stage is estimated by Winchell, 

 from changes of the course of the Mississippi River in and near the Twin Cities 

 of Minneapolis and St. Paul, to have been about 15,000 years. It seems to be 

 represented in the history of the Quaternary lakes Bonneville and Lahontan 

 by the stage of their desiccation between their previous prolonged stage of 

 high water and their ensuing higher but more brief rise of water; and it is 

 correlated with the Sangamon interglacial stage between the Illinoian and 

 lowan stages of glaciation. Its time is estimated to have been approximately 

 from 40,000 to 25,000 years ago. " 



7. MICHIGAN 



It is believed 165 that the older drift sheets extended over Michigan, the Kan- 

 san from Keewatin and the Illinoian from Labrador. Beds of muck and peat 

 have been found between drift sheets in deep borings as far north as Hopkins in 

 Allegan County, and near Shelby in Oceana County. These occur at a depth 

 of about 150 feet. It is not definitely known whether the overlying drift in- 

 cludes the lowan or is exclusively Wisconsin. At Ann Arbor borings struck a 

 much harder sheet of till than the Wisconsin in the lower part of the till. The 

 harder till is probably Illinoian. Its thickness at Ann Arbor is 30-40 feet, but 

 north of Ypsilanti it is 200 feet thick. 



In a later publication 166 Leverett refers certain old soils to the post-Illinoian 

 stage. These references include several mentioned above. The specific 

 localities are: 



Near Avoca, St. Clair County. 



East Fremont, Sanilac County. 



Near Hillsdale, Hillsdale County. 



Near Allegan, Allegan County. 



West of Shelby, Oceana County. 



JM Science, N. S., XXXVII, p. 457; Int. Geol. Congress, 12th session, Canada, 1913, 

 pp. 1-11. Many of the strata mentioned are referred in the present work to the Yarmouth 

 interval. See page 262. 



166 Leverett, 6th An. Rep., Mich. Acad. Sci., p. 105. 



166 Mich. Geol. Biol. Surv., Geol. Ser., No. 7, pp. 53-54. 



