192 
IOWA ACADEMY OF SCIENCES 
TESTIMONY OF FOSSILS. 
The patient and painstaking work of Prof. Shimek has done much 
in this direction, and we must acknowledge, that wherever a deposit 
contains only land shells, w'hich were clearly deposited with the for- 
mation, we must admit that it is quite certainly of aeolian deposition. 
But there are some uncertainties in the practical application of this 
principle. It must be admitted that there are unquestionable aeolian 
deposits including loess-like formations sometimes of great extent and 
thickness. There are such in the Black Hills. Such I have long recog- 
nized in the high points east of Haney’s in Mills county, Iowa, and there 
are such at many points along the bluffs north of there including the 
high pinnacles in Plymouth county which Dr. Bain so ably differentiated 
from the surrounding loess at lower levels. 
Nevertheless, for the wider application of the aeolian theory we 
must judge it unproven. 
Not only do the arguments already presented point in a contrary 
direction, but there are several considerations which weaken his argu- 
ment for the wider field and until they have been counterbalanced we 
must retain the older and more consistent view. 
1. The loess is acknowledged by all who are familiar with it to be 
subject to step faulting often to great depths. This is due to similar 
conditions to those which cause crevasses in glacier rapids. It occurs 
particularly on steep slopes when the lower portion has been rendered 
plastic by moisture. It is conceivable that molluscs frequenting the 
surface, might in this way be introduced to considerable depths. It may 
seem impertinent or unkind to even whisper that a trained observer 
should mistake such for fosslis, but it is only emphasizing the need of 
scientific caution in view of the next consideration. 
2. It is very difficult to distinguish disturbed and rearranged loess 
from that originally deposited. 
Loess washed by the rains into crevices, basins, or other depressions 
or that which flows as mud is' one hour plastic and mobile as water, the 
next has so reset that it is almost impossible to discover the former 
bounding surfaces. I know of no sure way unless some foreign object 
or some unusual tint be present to indicate. 
In this way may not shells have been entombed so gently that 
opercula and eggs may have been preserved as Prof. Shimek reports? 
Most of his fossil localities are on hillsides and near streams 
Until we have evidence from the central masses of loess, i. e. deep 
below a fiat surface, where fissuring or wash could not be postulated, 
there will be room for reasonable doubt. The wisdom of such suspen- 
sion of decision is the more apparent, when we remember how the 
majority of exposures in apparently equally favorable locations are 
found to be non-fossiliferous. Especially is this true of localities remote 
from main streams as Prof. Shimek himself testifies. 
Time permits but a word or two concerning two other points of 
minor importance. 
