252 The American Geologist April, i898 
Where peat is absent at this horizon there is often evidence of an 
ancient soil, humus stained and weather stained as is the case with 
modern soils. This soil, peat and forest horizon is correlated with the 
Aftonian inlerglacial deposits of southwestern Iowa. It has been en- 
countered in hundreds of wells and has been revealed in not a few 
instances in railway cuttings. Its development in the great railway cut 
at Oelwein, Iowa, is discussed in the Proceedings of the Iowa Academy 
of Sciences,* and its relations to the Sub-Aftonian and Kansan. till 
sheets are well set forth in the extensive series of well sections published 
by McGee.t 
Buchanan gravels were first recognized as a drstinct interglacial 
deposit at the gravel pit of the Illinois Central railway in section 32 of 
Byron township, Buchanan county, Iowa. A description of this type 
locality was read before the Iowa Academy of Sciences two years ago 
and was published in the American Geologist, t The beds to which the 
name was applied consist of stratified sand and gravel. The bedding is 
in places oblique, showing action of strong currents. Scattered through 
the deposit are bowlders ranging up to twelve or fifteen inches in diame- 
ter, and many of the bowlders still retain perfectly the facets and 
scratches due to glacial planing. They may have been transported by 
floating ice. At all events they have not been rolled or abraded to any 
appreciable extent. 
The materials composing the Buchanan gravels have been derived 
chiefly from northern sources. Furthermore they possess the charac- 
teristics of pebbles and bowlders found in the Kansan drift. Certain 
granites and other rock species are completely decayed, and crumble 
to fine particles on the application of slight force. Finally the gravels 
are exceedingly ferruginous and weather stained, particularly near the 
top of the deposit, the weathered portion taking on a characteristic rusty, 
reddish brown color. 
At the typical locality the Buchanan gravels rest on blue till of Kan- 
san age and are overlain by a bed of fresh lowan till from two to eight 
feet in thickness. The lowan till contains a great number of large 
sized, light colored granite bowlders, some of which are perched on the 
brink of the pit, while some have been undermined and have fallen to 
the bottom. The gravels here clearly lie between two sheets of till. 
The weathering, oxidation and decay the materials have suffered afford 
in some degree a measure of the length of the interglacial interval. Two 
years ago it was the current belief that the Pleistocene deposits of Iowa, 
except in the area occupied by the Wisconsin lobe, contained a record 
of two ice invasions and of two only. Accordingly the Aftonian gravels 
and soil beds which had previously been observed in Union county were 
assumed to lie between McGee's lower and upper till, and since the 
Buchanan gravels plainly occupied what seemed to be a similar position. 
they were first referred to the Aftonian stage. Our knowledge of Pleis- 
*Vol. IV, pp. 54-68 1897. 
tPleistocene History of Northeastern Iowa, pp. 515-540. 
tVol. XVII, p. 76, Feb. 1896. 
