IOWA \CADEMY OF SCIENCES. 25 



the Iowa strata tbau any of the other writers mentioned, and recognized out- 

 liers as far east as Guthrie county and as far south as Montgomery county. 



Recently numerous deep well records and Held observations have shown 

 that the Cretaceous deposits cover a much larger area than has hitherto 

 been recorded. The northwestern fourth or tifth of the State may now Ije 

 regarded as occupied by deposits of Cretaceous age. White, in considering 

 the Iowa Cretaceous, divided the beds as found iu tlie Sioux river region into 

 the Woodbury shales and sandstones and the luoce ramus beds. As recently 

 shown by Calvin the Woodlniry shales are equivalent to the Dakota sand- 

 stone and the Fort Benton shales of Meek and Hayden and the Inoceramus 

 beds are the same as the Niobrara of the same authors. Thus three of the 

 formations differentiated by Meek and Hayden are known to be well rep- 

 resented in Iowa. Daring the past season another formation of the Cretace- 

 ous age has been found to extend into Iowa. This is the Fort Pierre shale. It 

 was first noticed iu the State by Mr. H. F. Bain, who found it well developed 

 in the vicinity of Hawarden, in Sioux county, where it attains a consider- 

 able thickness. The easternmost location heretofore known showing the 

 Fort Pierre beds has been Yankton, South Dakota, at which place the deposits 

 are used largely in the manufacture of Portland cement. 



There is another division of the Cretaceous of the upper Missouri valley 

 which Meek and Hayden have recognized. This is the Fox Hills group. It 

 will be seen, therefore, that four out of the five Cretaceous formations of the 

 region are now known to extend into the State of Iowa. 



Incidentally it may be mentioned that the Niobrara chalks have been 

 recently recognized as far east as Auburn in the southeastern part of Sac 

 county, eighty miles east of any hiterto reported locality. The Cretaceous 

 deposits have also been extended southward by Mr. E. H. Lonsdale nearly 

 to the Missouri line. The gypsum deposits of Webster county, Iowa, are 

 also thought to belong to this age. It may not be out of place here to 

 mention the fact that iu the drifc of northwestern Iowa boulders have been 

 found consisting of soft friable ferruginous sandstone, highly fossiliferous, 

 the organic remains being characteristic Fox Hills forms. As remarked by 

 White the presence of the friable sandstone blocks indicates that they are 

 not far removed from their original localities. It would not, therefore, be 

 wholly unexpected should outliers of the Fox Hills group yet be found within 

 the limits of Iowa. 



DERIVATION OF THE UNIONE FAUNA OF THE NORTHWEST. 



BY CHARLES R. KEYES. 



One of the most striking features in the zoological history of the Missis- 

 sippi basin is the exceedingly rich and varied moluscan fauna, which is 

 characterized particularly by the Unio family, including all the common 

 river mussels. The great abundance of individuals, the large number of 



