5Q2 SAMUEL CALVIN 



relative age of drift. The splendid piece of work by Dr. R. T. 

 Chamberlin in the St. Croix region 1 shows how a very young 

 drift may exhibit no trace of lime, while a much older one may give 

 vigorous reactions. In each and every case the amount of calcium 

 carbonate present at or near the surface of a deposit of drift will 

 depend on the original composition of the till and the movements 

 of the ground waters. The same drift sheet gives very different 

 reactions in different localities. The work in Taylor County in 

 1 910 showed very large quantities of lime carbonate in the form 

 of segregated sheets and nodules, distributed along the joints in 

 the highly weathered zone of the old Kansan. The lime came 

 practically to the surface and was turned up among the grass roots 

 by the plow. Along the roadsides, where the highway had been 

 recently worked, it was breaking down to powder and mixing with 

 the crumbling clay; and a sample of the old drift taken at the very 

 surface might have given such energetic reactions to the man with 

 the acid bottle as to lead him to think that he was dealing with the 

 youngest glacial deposit in Iowa. Just why it is that both the old 

 Kansan and the young Iowan should be so very calcareous up to 

 the grass roots in some localities, while showing no traces of lime 

 in others, could be explained, in some cases at least, on the basis of 

 physical characteristics and relation to surface and sub-surface 

 drainage; but it will be sufficient here simply to record the fact 

 and repeat the obvious inference that acid tests applied to drift 

 sheets are of exceedingly small importance in the determination 

 of relative age. The acid bottle, intelligently used, has its place; 

 but the user must be careful to recognize its limitations. 



Among the evidences of youth in the Iowan drift is the fact that, 

 in its typical areas, it is uneroded and imperfectly drained. The 

 area selected for illustration in Fig. 7 of the article from the Ameri- 

 can Journal of Science, and again in Fig. 5 of the paper reprinted 

 from the Zeitschrift fur Gletscherkunde, and offered as "the type of 

 erosion" in the Iowan drift or as something "showing topography 

 of a so-called Iowan drift plain," is a somewhat unfortunate and 

 misleading choice for the reason that it is representative of but a 



1 Rollin T. Chamberlin, "Older Drifts in the St. Croix Region," Journal of Geology, 

 XVIII, No. 6, September-October, 19 10. 



