THE ILLINOIAN ICE INVASION 291 



Near Cooper a bed of muck was found between tills at a depth of 150 feet. 

 In Champaign County, 21 at Mahomet, a similar section occurs showing this 

 interval. 



Gravel 7 feet 



Pebbleless clay 3 " 



Brown and gray till 32 " 



Black muck 2 " 



Hard till 58 " 



Height of section 100 " 



The black muck or peat deposit near Mahomet contains a beetle fauna of 

 10 species which has recently been studied by Wickham. 21a The section from 

 which the beetles came has been studied by Dr. T. E. Savage who refers the 

 deposit to the Sangamon interval; it lies just above the Illinoian till and is 

 separated from the Wisconsin till by a slight development of loess-like silt. 

 Writing of the climate of the Sangamon, as indicated by the beetles, Wickham 

 says: "I think we are quite justified in assuming that conditions were, at any 

 rate, more rigorous than in southern Illinois at present. Probably they were 

 at least as severe as in Ontario at the date of formation of the Scarborough 

 beds. " Four families and seven genera are represented by the ten species. 



Carabidae Dytiscidae 



Carabus meander sangamon Agabus savagei 

 Palrobus henslmd " praelugens 



Platynus pleistocenicus Staphylinidae 



subgelidus Olophrum interglaciale 

 CItlaenius plicitipennis Chrysomelidae 



Donatio, styrioides 



Comparison with the beetles of the Toronto beds at Scarborough indicate 

 that none are identical as to species. It is probable that many peat deposits 

 of interglacial age contain the remains of insect fife, which will be of great 

 value for comparison with these deposits already studied, when they have been 

 given the same careful scrutiny. 



In Mercer County (Sect. 9, T. 13, R. 4) in the bluff bordering Pope Creek, 

 heavy beds of sandy marl occur, which contain some mollusks (Lymncea and 

 Succinea)P These beds apparently underlie Illinoian loess. In Boone Coun- 

 ty, 23 near Irene, a black soil is found separating Iowan from Illinoian till and 

 containing molluscan shells. 



Identifiable plants referable to the Sangamon appear to be rarely recorded 

 from Illinois. At Bloomington the two species noted below were recognized 



21 Op. tit., p. 703. 



- ,a Amer. Journ. Sci., iv, XL1V, pp. 137-145, 1917. 



22 Green, Geol. 111., IV, p. 302. 



23 Leverett, op. oil., p. 375. 



