ABSTKACTS AND DISCUSSIONS OF PAPERS 117 



to find a few yery small siliceous pebbles similar to those in the normal gumbo, 

 and it is thought that this loesslike clay is the result of changes that have 

 been going on at and near the surface of the gumbo during the great length 

 of time since the normal gumbo was formed. The loesslike clay which is now 

 found as a mantle on the Kansan drift on the slopes and divides that have 

 been brought by erosion considerably below the level of the original gumbo 

 plain is believed to be the product not primarily of wind action, although wind 

 may have been a factor, but chiefly the product of the weathering and con- 

 centration of the gumbo and to some extent of the underlying Kansan drift, 

 where erosion has not kept pace with the weathering. 



(4) The evidence indicates that the time taken to develop the present 

 topography from the gumbo plain stage, although it represents a great length 

 of time, is short when compared with the time taken to develop the gumbo 

 plain from the Kansan drift. It is thought that the formation of the main part 

 of the gumbo and the development of the present mature topography of the 

 Kansan drift were effected between the close of the Kansan epoch and the 

 advance of the Illinoian ice into Iowa ; in other words, during the Yarmouth 

 inter-Glacial epoch. All the evidence indicates that the Yarmouth epoch was 

 an exceedingly long interval of time. 



(5) Detailed chemical analyses of gumbo, loesslike clay, etcetera, are now 

 being made in the chemical laboratory of the University of Iowa by Dr. J. N. 

 Pearce. The results of these analyses will go far to strengthen or weaken the 

 interpretations given above from the field evidence. 



Presented in abstract extemporaneously. 



Discussion 



Mr. W. C. Alden : I would like to make a few remarks on the Iowan drift 

 in connection with Doctor Kay's paper. I have seen a number of exposures 

 of this clay on top of the Kansan drift, which, for want of a better name, we 

 have called ''gumbo." It seems to me a very important deposit. When first 

 seen I thought it must be distinct from the underlying till, inasmuch as the 

 till below it is oxidized, though the gumbo itself is mostly gray and unoxidized, 

 excepting at the top. On further examination, however, I do not feel sure of 

 its being distinct, and considerable evidence has been found indicating that it 

 really may be the weathered upper part of the Kansan till which has been 

 thoroughly leached of its soluble material and deoxidized. It is nowhere 

 laminated like a water-laid silt, where I have seen it. It generally contains 

 pebbles scattered sparsely throughout. The pebbles are mostly small and of 

 chert and quartz, with some quartzites and crystallines, the latter badly de- 

 composed. Rarely included boulders are found disintegrating and with feld- 

 spars decomposing to kaolin. Thicknesses of 15 to 20 feet of this clay are not 

 uncommon. There is no definite line at the base of the gumbo ; it grades into 

 the till below. I am not yet fully convinced that it is the residuum of weather- 

 ing of the upper part of the till, but there is much to suggest that this is the 

 case. Probably Doctor Kay's investigations will settle the matter. If it is 

 such, I think it indicates a very long time of exposure of the Kansan drift, 

 prior to the Illinoian stage of glaciation, since the gumbo is also found under 

 Illinoian till in Henry County, Illinois. It seems to make the Yarmouth in- 



