IOWA ACADEMY OF SCIENCES. 37 



were rain and snow, — there were pools, and springs, and 

 sti'eams, — and it would be strange indeed if some evidence of 

 water action, water-presence was not found. But the character 

 of these fresh water fossils, and their comparative scarcity, 

 indicate either that there were very few bodies of water, or 

 that the loess was deposited chiefly w^here there was no water. 

 Of the fresh water forms there remain to be considered the 

 species of Unio and Cav pelomn. These may be discussed together 

 for both genera are chiefly fluviatile, and are usually associated 

 in our streams, while the record of their occurrence in true 

 loess is about equally established. From two localities, only, 

 have specimens of loess Unionv^ce been reported.* Professor 

 Witter reportsf three species of Unio and one species of Mar- 

 gtritana from the loess of Muscatine. I All are recorded as 

 ' ' rare and local. ' ' 



Mr. H. Foster Bain, of the geological survey, furnished the 

 three species of Unio, represented by twelve valves, which are 

 reported in Table I, from Sioux City. The author does not 

 know whether any doubt exists concerning the correctness of 

 the reference of these forms to unmodified loess. § 



But granting that no such doubt does exist the evidence 

 furnished by them that the loess was deposited under fluviatile 

 conditions, is by no means conclusive. They are extremely 

 rare in proportion to other molluscs, and the occurrence of 

 such scanty material may be accounted for otherwise. The 

 author has a number of times found shells of Unios at a con- 

 siderable altitude above high water mark. The bluffs along 

 the Iowa river above Iowa City have furnished several 

 examples. Whether they were carried to their lodging places 

 by bird or beast could not be determined, but some of the shells 

 bore marks as of the teeth of a mammal. That there were 

 streams in loess times is evident from present river courses and 

 river valleys. That Unios occurred in these waters is quite 

 probable. That some of these should have been carried to 

 altitudes greater than those at which they were developed is 



*ro these should bs added a third locaUty. McGee, in U. S. Gaol. Sur., Vol. XI, p. 

 460, reports " fragile bits of shells of Unio or Anodonta" from Stone City, Iowa. 



tRep. U. S. Qeol. Sur., Vol. XI, p. 471. 



*For list of species see footnote (15) under Table I. 



§Slnce this paper was written Mr. Bain has submitted additional numerous val ves 

 of Unio from near the mouth of the Broken Kettle, Plymouth county, Iowa. A list of 

 the species is given in Tab^e III. With the Unios were associated a few shells of 

 Sitccinea Wneata and one specimen of Hclicodiscus lineatuf<, both being of the ordinary 

 loess type, The Unios were clustered in small heaps or pockets. Mr. Bain pronounce s 

 the deposit in which these shells, as well as those previously collected at Sioux City 

 were found, to be a terrace of modified loess. 



