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88 IOWA ACADEMY OP SCIENCE Vol. XXIV, l‘JJ7 
The persistency of these phenomena in cut after cut makes 
them of significance in reading the history recorded by the 
loess. The buff loess and the gray loess have heretofore been 
generally regarded as separate and distinct deposits, differing 
considerably in age. The buff loess has been thought to be of 
Iowan age and younger, while the gray has been held to be of 
approximately Kansan age, it being held that the gray prob- 
ably has the same relation to the Kansan drift as the buff seems 
to have to the Iowan drift. 
These conclusions, however, do not seem to the writer to be 
well based. Of the many exposures examined, on the east and 
south sides of the Iowan area, there was not a single one which 
showed good evidence of an interval of time between the depo- 
sition of the gray and the buff. There is no zone of leaching 
at the top of the gray, such as would be expected if the two 
deposits belong to two different epochs, nor is there any other 
strong evidence of weathering effects that would differentiate 
the two. Indeed there is a continuance of lime carbonate par- 
ticles and shells from the gray up' into the buff, and in most 
cases there is a transition in color. It is true that in some 
instances rusty streaks occur at the contact, but these were 
found also indiscriminately at any horizon. In view of these 
features of gradation and the absence of any that distinctly 
separate the two in terms of time intervals, the writer has 
become convinced that the two are of the same geological age, 
that the mass of the loess was originally gray, and that the 
buff is to be regarded merely as the oxidized phase of the gray. 
Another important historical point to be noted from a study 
of the weathering of the loess is that the leached zone records 
the fact that the loess has been subjected to the solvent action 
of ground water for a sufficient length of time for the cal- 
careous particles and snail shells to be dissolved out to a depth 
of several feet. Fossils are not seen in many shallow cuts for 
they occur only in the zone which has not been leached. One 
must bear in mind, however, the possibility that the upper 
part of the loess was deposited as a noncalcareous clay. This 
may be true of some of the leached zone, but it would be an 
extreme view to assume that the ground water has performed no 
work since the loess was deposited, especially if the mass of the 
loess is pre-Wisconsin in age as will be shown later. But aside 
