IOWA ACADEMY OF 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 facD 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 water, 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. Succinca vcrilli and Pupa 

 decora should be stricken from the list, and Pupa holzingcri Sterki should he 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. II pp. 95 and 96. 



5 Ibid. p. 93. 



>;See also Prof. K. D. Salisbury's report in Ark. Geol. Survey, Vol. II, pp. 325, 226. 



