490 IOWA ACADEMY OF SCIENCE Vol. XXVI, 1919 



out a break below the Cedar Valley and at all other points where the 

 basal beds of the Cedar Valley are exposed there is no erosion con- 

 tact between them and the subjacent beds. Granted that the Bran- 

 don contact is an erosional unconformity, it would seem strange 

 that the resistant Davenport beds should be entirely removed, leav- 

 ing the relatively unresistant shale in the form of steep-sided rem- 

 nants as we have it at each of the three exposures. Moreover, the 

 shale must have been lifted by an upwarp of 125 feet to bring about 

 the relations indicated; (2) the fact that the Sweetland Creek and 

 State Quarry lie unconformably in depressions in the Cedar Valley 

 and the additional fact that certain resemblances exist between the 

 faunas of the Independence and Lime Creek shales lend plausibility 

 to the view that the Independence shale deposits are remnants of a 

 formerly wider distribution of the Lime Creek. Against this view 

 it should be pointed out that where the Lime Creek shales are typ- 

 ically developed, as in Cerro Gordo, Floyd and Butler counties, the 

 fossiliferous part of the Lime Creek — at least that part containing 

 the Independence-like fauna — is underlain by scores of feet of rela- 

 tively barren plastic shales and these in turn are separated from the 

 Cedar Valley by the Nora limestone^ which in places is twenty feet 

 thick. It would seem that some part of the Nora or of the plastic 

 blue shale should fill a part or all of these depressions rather than 

 they should be filled with the fossiliferous shale occurring below 

 the Owen limestone near the top of the Lime Creek section. The 

 fossils of the Independence, when they are critically studied, are 

 seen to be quite distinct from these of the Lime Creek. It is true 

 that a few species, such as Strop honclla rcvcrsa, Doiivillina arcuata, 

 Atrypa reticularis, A. hystrix, Macgcca soUtaria, and possibly a few 

 others occur in both formations. A brief study, however, enables 

 one to distinguish those from either formation readily. The Inde- 

 pendence species are invariably smaller and there are other differ- 

 ences. Stropheodonta calvini and Douvillina variabilis are the com- 

 monest species in the Independence — the forms which have gone 

 under these names from the Lime Creek are specifically distinct from 

 them and the same is true of some others. Moreover, the index fos- 

 sils of the marly shales of the Lime Creek, Spirifer hnngcrfordi, S. 

 orcstcs and 6". zvhitncyi do not occur in the Independence, while the 

 conmion little Ortliis {Dahnanclla) infcra 'and the rarer Gypidida 

 mimda as well as the atypical Marti^iia snbnmbona have no represen- 

 tives in the Lime Creek. Other equally striking absences and differ- 

 ences could be given but the instances cited are sufficient to confirm 





'Science, n. s. Vol. XXXVI, 1912, pp. 569, 570. 



