INDEPENDENCE SHALE NEAR BRANDON 489 



A list of the more common species collected at the three localities 

 may be of interest. The brachiopods greatly predominate. 



Zaphrentis sp. 



Macgcca solitaria (H. & W.). 



Orfhis (Dalmanella) infera Calvin. 



ScIiisopJwria cf. striatiila (Schlotheim). 



Strophcodonta calvini S. A. M. 



Strophonella reversa Hall. 



Lcptostrophia cf. canace (H. & W.). 



Doiwillina arcuata (Hall). 



Doiivillina variabilis (Calvin). 



Prodnctella hallana Walcott. 



Strophalosia n. s. 



Hypothyridina cuhoidcs (Sowerby). 



A try pa reticularis (Linne). 



A try pa hystrix Hall. 



Spirifer sp. 



Martinia subumbona (Hall). 



Cyrtina n. s. 



Crinoid stems. 



Plate of crinoid. 



Tcntaculites sp. 



Ostracoda (undet.). 



The low monoclinal dip of the Paleozoic strata of Iowa is to the 

 southwest and amounts to ten to fifteen feet per mile. The Bran- 

 don exposures of the Independence shale are twelve to fifteen miles 

 southwest of the artificial exposures at and near the O'Toole quarry. 

 According to an unpublished topographic map of Iowa by Dr. James 

 H. Lees, the altitudes of the Brandon and Independence exposures 

 are each close to 900 feet above sea level. Hence, at Brandon, other 

 things being equal, the Independence shale should be at least 125 

 feet below the surface. Its anomalous occurrence on a level with 

 the basal Cedar Valley may be explained : (1) as a local unconform- 

 ity in which the Lower and Upper Davenport beds are wanting and 

 with the Cedar Valley resting on the Independence shale; (2) as a 

 post-Cedar Valley deposit laid down in the erosion hollows or other 

 depressions in its surface; (3) as a filling thrust up into irregular 

 openings in the Cedar Valley at the time of the brecciation of the 

 lower Devonian terranes. 



A brief discussion of the three hypotheses brings out (1), at In- 

 dependence only fifteen miles away the Davenport beds occur with- 



