THE ORIGIN OF GUMBOTIL 125 



northern Missouri, and other till sheets elsewhere, believes that 

 the upper parts of the tills have been, from the times of deposition 

 of the drifts, somewhat different from the middle and lower portions 

 of the drift.^ 



It should be stated that, although it is believed that gumbotil 

 is essentially the result of chemical weathering of glacial till, it 

 is recognized that wind action, freezing and thawing, burrowing 

 of animals, slope wash, and other factors may have contributed to 

 the formation of these gumbotils. 



In a subsequent paper attention will be directed to the fact that 

 the gumbotils, on account of their distinctive characters, wide 

 distribution, and topographic positions, are the most satisfactory, 

 criteria that have yet been found for differentiating the older drifts. 

 Furthermore, since the gumbotils are the result of changes which 

 took place in interglacial times, they may be considered in relation 

 to the problem of the relative durations of the interglacial epochs. 



The gumbotils strengthen the view now generally accepted that 

 the history of the Glacial Period involves, not a few thousand years 

 but probably hundreds of thousands, and possibly millions, of years. 



' E. W. Shaw, "Characteristics of the Upper Part of the Till of Southern Illinois 

 and Elsewhere," Abstract, Bull. Geol. Soc. Amer., Vol. XXIX (1918), p. 76. 



