150 Scientific Intelligence. 



In the Devonian system an unconformity is recognized as sepa- 

 rating the Devonian from the Silurian formation, and the lowest 

 member of the Devonian in tbis county is the peculiar " Fayette 

 breccia" described by Norton from the Lime county exposure 

 (Iowa Geol. Surv., vol. iv, p. 157). This is shown, both by its 

 fossils and by the presence of the Otis and Independence beds 

 below it in other regions, to be Devonian and near to the horizon 

 of the Hamilton of New York. 



Another unconformity is recognized higher up in the Devonian, 

 separating the Cedar Valley formation from the State Quarry. 

 The characters of this latter formation are so peculiar that special 

 attention may be called to them by a few quotations : 



" At the state quarries, or North Bend quarries, in sections 5 and 

 8 of Penn township, there is a body of limestone of Devonian 

 age, possessing marked characteristics which set it off sharply 

 from the rest of the Devonian in Iowa. The formation has a 

 thickness of about forty feet. At present there is some uncer- 

 tainty as to its exact taxonomic relations. 



" On fresh fracture the state quarry rock is light gray in color. 

 In texture it varies somewhat in different beds, but near the 

 middle of the' formation it is composed of coarse, imperfectly 

 comminuted fragments of brachiopod shells cemented together, 

 the spaces being filled with interstitial calcite. Among the recog- 

 nizable species of shells Atrypa reticularis is the most common, 

 but some beds contain very large numbers of Dielasma ( Crancena) 

 ioioensis. At some horizons shells of an Orthothetes are common. 

 Orthis impressa is not rare and Rynchonella pugnus (Pugnax 

 pugnus) occurs occasionally. The shells, or fragments of shells, 

 making up the limestone are not embedded in a matrix. They 

 are simply piled on each other and cemented together in a man- 

 ner illustrated by the formation of the modern coquina along the 

 east coast of Florida. The rocks near the middle of the state 

 quarry beds are a brachiopod coquina having the interstices com- 

 pletely filled with crystalline calcite. * * * 



"The anomalous relations of this formation, the limited areas to 

 which it is confined, the abrupt manner in which it appears and 

 disappears, sometimes at the level of one member of the Cedar 

 Valley section and sometimes at the level of another, all lead to 

 the conclusion that it was deposited unconformably on the Cedar 

 Valley limestone after the lapse of a considerable erosion inter- 

 val. The same view is even more strongly suggested by the fact 

 that in certain respects the fauna of the state quarry beds is 

 unique. The deposit near Solon furnishes Pugnax pugnus Martin, 

 Melocrinus' calvini Wachsmuth, and a very peculiar stromato- 

 poroid, none of which is found in the other Devonian formations. 

 Of other species that have a greater vertical range, as for 

 example Atrypa reticularis, there is sufficient variation to dis- 

 tinguish them from individuals of the same species found at other 

 horizons. The Orthothetes, so common in the beds in section 5 

 of Penn township, is associated with Pugnax, and like it is 



