70 IOWA ACADEMY OF SCIENCES. 



pebbles rarely exceed three-fourths of an inch in diameter and 

 the majority are not more than half an inch. Bowlders such as 

 occur at the typical exposure are almost unknown. Beds of 

 the same character form a broad terrace along the valley of the 

 Wapsipinicon from Littleton to Independence, and are con- 

 tinued up every lateral valley for a distance of some miles. 

 The greater abundance of sand, the regular bedding, the 

 smaller size of the pebbles making up the gravelly portion of 

 the deposit, and the scarcity of bowlders, dilferentiate the 

 valley gravels from those occurring on the highlands. Further- 

 more the upland gravels are weather-stained and oxidized to a 

 much greater depth than those found in the valleys, doubtless 

 due to the fact that the coarser nature of the deposits offers 

 greater facilities for the penetration of oxidizing and weather- 

 ing agents There is, however, a perfect intergradation of the 

 two phases, and both are alike covered with a mantle of lowan 

 drift so far as they lie within the lowan area. 



The use of the lerm Buchanan as a name for an interglacial 

 stage is open to criticism. It came into use tentatively before 

 the recognition of the Illinoian drift, as .a stage distinct from 

 either Kansan or lowan, had been published, and when the 

 whole period of time between the retreat of the Kansan and 

 invasion of the lowan ice was supposed to be a single, uninter- 

 rupted, interglacial interval. It was first used in the precise 

 sense in which the term Af tonian was originally used, and as a 

 substitute for that term when it was shown that the Aftonian 

 soils and gravels preceded the Kansan stage. Since the recog- 

 nition of the -Illinoian glacial stage the term has been used for 

 the interval following the Kansan in publications by Chamber- 

 lin, Calvin and Scott. No great objection to its continued use 

 can be urged. In fact it is much to be desired that names once 

 introduced should remain undisturbed, but it may after all be 

 a decided gain to Pleistocene geology to select a name for the 

 interval between the Kansan and Illinoian from some locality 

 where true interglacial deposits are clearly intercalated 

 between the Kansan and Illinoian sheets of drift. 



