574 E. C. CASE 



Measures of Vermillion Co., in the Report of the Geological Survey of Illinois by 

 A. H. Worthen, Vol. IV, p. 245. It is about 11 1 feet, averaging different locali- 

 ties, from the summit of the series, and 2,0992 feet from the base. Two insignifi- 

 cant beds of corals [misprint for coaI\ occur above and the following genera of 

 invertebrate fossils: Productus, Spirifer, Athyris, Terebrahda, Hemipronites, 

 Retzia, Zeacrinus, Cyathaxonia, Discinia, Lingula, Cardiomorpha, Orthoceras, 

 and Nautilus. Several of these genera are found in the Zechstein, while others 

 belong to the Coal Measures and below them. 



In another paper of the same year he says:^ 



Twenty species have now been obtained from the Clepsydrops shale, the 

 exact geological position of which remains to be accurately determined. Dr. 

 Winslow informed me that they are the bed No. 15 of Professor Bradley's section 

 of the Carboniferous rocks of Vermillion Co., Illinois. This places them at the 

 summit of the Carboniferous series, below two thin beds of coal. I am now 

 informed that this portion of Professor Bradley's report is not correct, and that 

 No. 15 occupies a much higher position than he assigns to it. It lies uncon- 

 formably above the meron sandstone of Mr. Collett, which deposit is above the 

 Coal Measures and unconformable to them. The stratigraphic evidence is thus 

 confirmatory of that derived from paleontology, that the Clepsydrops shale 

 occupies a position in the scale above the Coal Measures. 



A page or two farther on in the same article he correlates the 

 Texas and Illinois horizons (p. 193): 



The discovery of a species of the genus Clepsydrops in Texas, in a formation 

 hitherto regarded as Triassic, adds weight to the view above expressed, that 

 the Clepsydrops shales of Illinois belong either to the Triassic or Permian forma- 

 tions. 



In 1878 he definitely asserted the Permian Age of the beds:^ 



The Texan genera of this group (Pelycosauria), so far as yet known, are 

 about equally related to the Ural and South African types. The age of the 

 former deposit is the Permian, which includes, according to Murchison, the 

 Todthegende and the Zechstein of Thuringia. The age of the South African 

 beds is uncertain but is suspected by some authors to be Triassic, and by Owen 

 to be Paleozoic. In discussing the Clepsydrops shales of Illinois, which had 

 been referred to the Coal Measures by previous investigators, I left the question 

 open as to whether they should be referred to the Triassic or the Permian forma- 

 tions. The evidence now adduced is sufficient to assign the formation, as repre- 

 sented in Illinois and Texas, to the Permian. Besides the saurian genera men- 

 tioned above, the existence of the icthyic genera Janassa, Ctenodus, and Diplodus, 

 in both localities, renders this course necessary. 



I Am. Phil. Soc. Proc, 1877, Vol. XVII, p. 182. 2 Ibid., p. 350. 



