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IOWA ACADEMY OP SCIENCE 
to furnish good drainage, but not so much exposed to sun and hot winds 
that a continuous plant covering is impossible. 
The combination of the favorable results of all these conditions can alone 
bring about the accumulation of dust, and this fact is sufficient response to the 
statement that “it would seem that the loess, if of eolian derivation, should he 
as widespread over the country as the channelless currents of the air which 
laid it,” a statement which would have significance only if nothing besides wind 
was necessary to form loess! 
The drifting of snow furnishes an illustration of the manner in which this 
combination of circumstances operates. (See Plate XI, fig. 2.) The snow is 
blown from fiat exposed places, and lodged where there is anchorage — either 
plant or otherwise. Snow falls equally over a forest surface, but drifts in un- 
equal masses in more open territory. In this there is certainly suggestion to 
the student of loess. 
Further suggestion is offered by sand dunes. If Professor Norton has 
trouble. in understanding how one elevation might he loess-covered and another 
in the same general territory bare, he might consider why in a given sand dune 
area one dune is often covered with vegetation, and sometimes a veneer of soil, 
while another nearby is hare, or nearly so, and why the intermediate depressions 
are sometimes quite or nearly devoid of sand, as in the White Sands desert in 
New Mexico, and elsewhere. 
The fact is that the very conditions which seem to have troubled Professor 
Norton are so consistent with those of areas undoubtedly materially influenced 
by wind that they furnish strong support to the aeolian hypothesis. 
Another objection is made, in the paper cited, to the suggestion that loess is 
in part accumulated in forests, on the ground that there are forests on the 
Wapsipinicon bottoms which have no loess. Here sight was lost of the fact that 
these forests are much more modern than the latest drift; that the bottom lands 
are subject to frequent overflow, this introducing an important element which 
does not operate on the uplands; and that the combination of circunistances 
already noted is necessary to form loess. Loess materials are no doubt 
gradually carried into these forests, but the accumulation is so slow that 
through the agency of floods, even when occurring at long intervals, this is 
lost in the mass of alluvium transported by the stream. 
However, it should be noted that at no time has it been claimed that loess 
was formed in forests alone. Any vegetation will serve as a holdfast, but in 
the forest the accumulation will be more uniformly blanket-like, as already 
stated. 
The final objection that if the loess had been formed in a forest rapidly there 
should be an accumulation of carbonaceous material, and if slowly that it 
should have been decalcified through the action of humous acids, etc., is of little ■ 
weight. The aeolian hypothesis postulates a very slow accumulation of loess, 
hence the first part of this objection need not be considered. The second part 
would be more valid if water acted only downward in the soil, and if calcium 
carbonate was not soluble in water. But "^o long as such a mobile agent as 
water, often laden with calcareous niaterial in solution, can now be drawn up- 
ward by capillarity, the presence or absence of calcium carbonate in the soils 
and subsoils can have little bearing on the question of the origin of the loess. 
But again it should be remembered that at no time has it been argued that 
