Geological Papers. 105 



not deposited rapidly enough to produce deep and wide beds of 

 loess. Its blanket-like distribution, its evanescent relations to 

 the soil above, and the undoubted water or ice deposits below 

 strongly suggest that the material springs from the finely sub- 

 divided glacial debris scattered during the periods following 

 the ice invasions. Touching the further question of evidence 

 that this loess is seolian instead of aqueous in origin, the follow- 

 ing points can only be summarily stated: (a) The loess of 

 Minnesota does not occur in any one of the 1000 lakes of that 

 state, existing or extinct, whose deposits have been described. 



(b) It does occur on the higher levels of the glacial drift. 



(c) When in relation with dune sands, it is found higher than 

 they; whereas, as a water deposit it would be lower — that is, 

 farther from the shore-line of deposition, (d) It is frequently 

 liable to carry loam within it, thus pointing to zones of vegeta- 

 tion.'"' 



Concerning the loess of Iowa, Mr. Shimek says :" "It will be 

 observed that the proportion of local aquatic shells found in the 

 loess here and elsewhere'" is comparatively insignificant, and 

 what is true of species applies with even greater force to in- 

 dividuals. The fossil shells of aquatic species occur very spar- 

 ingly, and even the aquatic fossils found belong to the fauna 

 of small ponds or streamlets, which may, and often do, re- 

 main dry during the greater part of the summer, and their 

 presence in nowise proves that large bodies of water existed 

 where the loess was deposited. Indeed, the total absence of 

 species which are truly fluviatile, or which at least prefer large 

 bodies of water, would point to the contrary conclusion. Had 

 large streams or other bodies of water existed where the loess 

 is deposited, thus furnishing conditions favorable to a fluvia- 

 tile fauna, it is reasonable to suppose that some of these shells 

 would be found fossil to-day to relate the story of the condi- 

 tions under which they existed ; yet no such evidence has ever 

 been found in undoubted, undisturbed loess, and the con- 

 clusion that such large bodies of water did not exist where 

 loess is found is irresistible. Indeed the moluscan fauna of 

 the loess points to comparatively dry upland terrestrial con- 

 ditions, such as exist over the greater part of Iowa to-day. It 



13. In this paper paragraphs within quotation marks are usually quoted direct, 

 though not always. In all cases, however, where the quotation marks are used they 

 are in the main the language of the author quoted. 



14. Amer. Geol., vol. XXXVIII, 1901. 



15. Given on the Identification of Recent and Fossil Molluscas at Iowa City. 

 See Amer. Geol., vol. XXVIII, pp. 345-357. 



