IOWA ACADEMY OP SCIENCES. 
83 
First . — The land area during the period of the formation of 
the loess was large as is shown by the remains of great num- 
bers of terrestrial molluscs.^ 
Not only the number of species but the number of individuals 
of the terrestrial forms is much greater, a fact especially sig- 
nificant since the pond molluscs are all very prolific and had 
the conditions been favorable to their development much 
greater numbers of the fossils should occur. 
That the shells of the loess were deposited in situ and were 
not carried any great distance by water has already been 
pointed out by the writer.^ 
Second . — The occurrence of dry region molluscs, such as Suc- 
cinea lineata. Pupa atticola, Patula cooperi, etc., has also been 
pointed out. ® The great majority of the remaining species occur 
now in a living state throughout Iowa and eastern Nebraska, 
more particularly in wooded regions. Most of them do not 
seem to require an excess of moisture, but thrive under present 
conditions. 
Third. — The deposits often occur so high above the surround- 
ing region that it is difficult to conceive of the manner in which 
water laden with the fine silt could reach the places of deposi- 
tion. 
Fourth . — The siliceous and other particles which the loess 
contains are generally angular and often show a freshness of 
fractures which would scarcely appear in particles which had 
been rolled and washed about by the waters.*^ 
Fifth. — The distribution of the loess is better accounted for 
by the consideration of the action of winds, and by the distri- 
bution of the forest areas, as will be shown in the following 
pages. 
The fact that stratification and lamination sometimes appear 
in the loess, showing the action of w^ater, together with the 
presence of aquatic molluscs, can also be accounted for under 
the wind theory; for, as now, so at the time that the deposits 
were being formed, ponds and lakes of various sizes were scat- 
tered over the state, and much of the dust carried out in clouds 
over these bodies of water would have been deposited in them. 
3See Bull. Nat. Hist. State Univ. Iowa, Vol. I. p. 209, et seq. Succinea verilli and Pupa 
decora should be stricken from the list, and Pupa holzingeri Sterki should be added. 
This species is rather rare in the loess of Nebraska, but in the living state it is quite 
common in both Iowa and eastern Nebraska. 
iBull. Nat. Hist. S. U. I. Vol. H, pp. 95 and 96. 
^Ibid. p. 93. 
cSee also Prof. R. D. Salisbury’s report in Aric. Geol. Survey, Vol. II, pp. 225, 226. 
