22 IOWA ACADEMY OF SCIENCKS. 



At the town of Hot Springs some portions of tiie valley are occupied by 

 horizontal beds of a very coarse conglomerate that lies uncouformably on 

 the folded and tilted Red Beds. The thickness of the conglomerate is about 

 forty feet. It is composed of fragments of all the harder formations from 

 the crystalline rocks at the center of the uplift to the purple limestone of 

 the Red Beds and the quartzite of the Cretaceous. When the conglomerate 

 was deposited the valley had essentially its present depth. In some places 

 the streams have just fairly completed the work of cutting through the 

 conglomerate, in other places they have cut twenty or thirty feet below 

 its base. This conglomerate is probably the equivalent of that lying at 

 the base of the White river Miocene. If so it would indicate an enormous 

 amount of erosion between the beginning and middle of the Tertiary as 

 compared with the amount accomplished since. 



Returning linally to the main object for which these observations were 

 undertaken, it is clear that BenneUites dacotensis Macbride, belongs to the 

 Cretaceous period, and the evidence is practically conclusive that the exact 

 horizon at which the individuals of the species were imbedded is represented 

 by the uppermost layers of the Dakota sandstone. 



NOTES ON THE LOWER STRATA OF THE DEVONIAN SERIES 

 IN IOWA. 



BY VTILLIAM HARMON NORTON. 



In a report recently made to tlie State Geological Survey, the wi'iter com- 

 municates in detail some facts regarding the breeciated zone of the Devonian 

 in Linn county, Iowa, and the tei'ranes subjacent. The following is in part 

 a brief summary of this report: 



In the breccia which occupies the same horizon from Davenport to Fay- 

 ette, and which has been termed by McGee the Fayette breccia, four stages 

 are discriminated. 



The fourth, or upper stage, involves in Linn county to a greater or less 

 extent several life-zones of the Cedar Valley limestone, including the hor- 

 izons of Acervtdaria davidsoni (E. and H.), Phillipsastrea gigas (Owen), Spir. 

 ijera 2)ennata (Owen), and IS pirifera dimesialis (Hall). Matrix and fragments 

 are alike being fossiliferous and shaly, and the fragments are usually large 

 and often but slightly disturbed. 



The third stage is distinguished by the predominance of fragmental 

 masses, often large and rectangular, of a tough, grey, crystalline or serai- 

 crystalline, heavily bedded limestone, containing a distinct fauna, of which 

 a large Oyroceras and Rhynchonella intermedia {Bnxv'xs) are the most charac- 

 teristic fossils, and Oypidula occidentalis (Hall) and Orthis macfarlnndi 

 (Meek), the most common. The limestone of which these fragments is com- 

 posed is not found in place in Linn county. 



