DEVONIAN FISHES OF IOWA 45 



II. 

 Stratigraphy of the Devonian fish-bearing beds of Iowa. 



The assemblage of sediments representing the Devonian sys- 

 tem in Iowa forms a belt averaging fifty miles in width, stretch- 

 ing along the Cedar river from the Minnesota line to Muscatine 

 comity, and extending thence eastward into Illinois. The larger 

 part of these rocks consists of limestones and shales whose bed- 

 ding, in general conformable, gives indication of continuous de- 

 position, whose faunal content is on the whole fairly character- 

 istic of the Middle Devonian, and yet none of whose parts can 

 be definitely correlated with formational units referred to the 

 same system in New York. The reason for this non-homogeneity 

 in the faunal characteristics of the two areas, namely the eastern 

 or "Ohian" as it has been termed (known also as the ''Appal- 

 achian"), and the western interior or "Dakotan", lies in the 

 fact that these were distinct geographical provinces throughout 

 the Devonian. They remained, in fact, completely separated 

 from each' other until towards the close of the Middle Devonian, 

 and thereafter communication was maintained between them 

 by means of a comparatively narrow passageway extending 

 through Illinois and Wisconsin. These conditions are well por- 

 trayed in the palgeogeographic maps given in Plates XIV-XVI, 

 hitherto unpublished, and for whose use we are indebted to 

 Professor Schuchert. 



A tripartite division of the Iowan Middle Devonian rocks into 

 the Wapsipinicon, Cedar Valley, and Lime Creek stages was 

 first proposed by Professor Calvin in 1878. It was pointed out 

 also by the same author that, owing to migration of species, the 

 faunas of the summital (Lime Creek) and basal shales (Inde- 

 pendence beds of the Wapsipinicon stage) are substantially iden- 

 tical, and that the fauna of the Cedar Valley limestone corre- 



