78 PROCEEDIXGS OF THE SAIXT LOUIS MEETIXG 



6. The loess has two phases, the upper of which is buff in color; the lower 

 is gray. In many places the buff loess is leached for a few feet from the sur- 

 face; in a few cuts the depth of leaching is about 15 feet. The buff and the 

 gray phases of the loess are closely related, and the evidence indicates that 

 their differences are the result of chemical reactions rather than of different 

 epochs of deposition. 



Presented in full extemporaneously. 



Discussion 



Mr. Frank Leverett inquired of Professor Kay whether he had found evi- 

 dence that the gumbotil was originally different from typical boulder-clay. 

 In reply to a question by Professor Rich. Mr. T>everett mentioned the wide 

 lowlands bordering the lower courses of the Embarrass and Kaskaskian and 

 other rivers in southern Illinois as examples of areas that are not undergoing 

 stream trenching because they are too flat for streams to form such trenches. 



In reply to Mr. Leverett, Professor Kay stated that the boulder-clay from 

 which the gumbotil has been derived may have differed from typical boulder- 

 clay, but he had no distinctive evidence in favor of this view. His impression 

 was that in the case of the lowan and Wisconsin drifts, which are too young 

 to have had a gumbotil developed on them, the drift at and near the surface 

 does not differ in any important respect from the drift which is deeper below 

 the surface. 



Dr. J. L. Rich : The speaker's interpretation of the relations of the two 

 gumbotils to their underlying tills and his explanation of their origin involves 

 a particular series of events twice repeated in identical order, namely, a long 

 period of weathering under conditions precluding active stream erosion, fol- 

 lowed by dissection, presumably resulting from diastrophism. It is difficult to 

 believe that such a repetition of events is a purely accidental coincidence. If 

 not, it seems to me that either the explanation is imperfect or there must be 

 some causal relation between the periods of glaciation and of lagging diastro- 

 phism which would be of great significance if discovered. 



In reply to Doctor Rich, Professor Kay stated that he recognized the full 

 significance of the point raised, but he was unable to offer an explanation of 

 the field evidence that would not involve the peculiar series of events that 

 seem difficult to believe. But are not other series of events of the Pleistocene 

 equally difficult to believe? What a succession of events is involved in the 

 now generally accepted five glacial epochs and the four interglacial epochs ! 



Mr. J. E. Todd; 1. I would like to inquire how Doctor Kay harmonizes his 

 statement of the close similarity of Nebraskan and Kansan tills with state- 

 ments of earlier students of the subject that they were easily distinguishable 

 by color and composition. 



2. I would like to call attention to the occurrence near Aikins, Pottawatomie - 

 County, Kansas, of black boulders of supposed Nebraskan till in Kansas till. 

 Furthermore, erosion is at an altitude considerably higher than central Iowa. 



In reply to Professor Todd, Professor Kay stated that the earlier students 

 of the drifts did not have opportunity to study the Nebraskan and Kansan 

 drifts in all their relationships in widely distributed areas. Many important 

 exposures have been made available for study only during the past few years 



