The Dipneusti and Crossopterygii 297 



such marine organisms as Stromatopora. Accordingly 

 Eastman states that Ptyctodtis, Rhynchodus, species of 

 Dinichthys and Dipterus were found in "Cedar Valley 

 Limestone, Iowa." 



But more careful and extended study of these beds by 

 J. A. Udden shows that the Cedar Creek limestone is a 

 marine formation in its lithologic, its organismal, and its 

 stratigraphic continuity. An evident break then occurred 

 in deposit, due to elevation and succeeding denudation of 

 land. Next a thin seam of black bituminous material was 

 laid down neatly on the abraded irregular surface of the 

 Cedar Valley rocks. This was succeeded by a greenish 

 argillaceous dolomite, that formed the fish conglomerate, 

 while this again passed up into a greenish gray shale with 

 fish teeth and "impressions of vegetable tissue." This 

 again was succeeded by a Lingula-limestone, and it by still 

 higher beds of marine character. These Udden calls col- 

 lectively the "Sweetland Creek Beds." Though only a sug- 

 gestion, the writer would propose: that the Cedar Creek 

 Beds represent the Erian of Ohio rocks; that after deposi- 

 tion of them a sudden upheaval of land took place, and 

 denudation of it set in. By subsequent volcanic agency the 

 land became covered by freshwater, a multitude of fresh- 

 water chimaeroids — Rhynchodus and Ptyctodiis — as well 

 as arthrodires and dipnoans, were later destroyed, and 

 while the decaying carcases rotted for a few weeks till 

 teeth and bones were set free, all were entombed in a 

 volcanic dust that formed the "greenish stony argillaceous 

 dolomite" which became the inorganic matrix. 



All of the above freshwater deposits might represent 

 a thinned-out western representative of the Cleveland shale, 

 while, the entire series, from the lowermost beds of the 

 Cedar Creek limestone to the marine summit series of the 

 "Sweetland Creek Beds" constitute what some geologists 

 have united as the "Hamilton Group." So instead of the 

 apparent anomaly of finding arthrodires and marine organ- 

 isms in mixed organic relation, the above beds, when ac- 

 curately interpreted, form a welcome verification of the 

 writer's fundamental thesis. Recent complete lists of 

 North American devonian arthrodires and their stratigra- 



