604 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



on Weller^^ called attention to "the correlation of the Pella beds 

 with the Ste. Gene\'ieve" of Illinois and Missouri; in addition, 

 field work by Van Tuyl in southeastern Iowa has shown that the 

 Pella beds are formationally distinct from the subjacent St. 

 Louis. It was first Weller/* and later Weller and Van Tuyl,^^ 

 who called specific attention to the existence of Ste. Genevieve 

 (Pella) beds at Fort Dodge although White, quoted above, had 

 recognized nearlj^ fifty years before the faunal similarity of the 

 marl at Fort Dodge and of the St. Louis of southeastern Iowa 

 as the latter formation was then delimited. 



The fauna of the marly zone presents some interesting features. 

 It is composed almost entirely of brachiopods, in addition to 

 which are a few bryozoa, fragments of a trilobite, a few thin 

 columnals of a slender crinoid stem, and some inconspicuous at- 

 tached and burrowing forms. Of the brachiopods, the index spe- 

 cies of the Pella beds, Spirifer pellaensis Weller and Pugnoides 

 ottumwa (White), make up about niliety per cent of the entire 

 assemblage. The next commonest species is Composita trinuclea 

 (Hall) while the remaining forms occur rather sparingly. The 

 absence of corals and molluscs and the meager representation of 

 echinoderms and arthropods point, it would seem, to an environ- 

 ment unfavorable to these groups. The shaly nature of the 

 marly beds indicates a muddy and more or less inhospitable sea 

 bottom while the reddish color of much of the formation suggests 

 to many geologists a comparatively arid climate at the time of 

 their deposition. Moreover, the absence of molluscs plus the evi- 

 dence offered by the brachiopods indicate that the fossiliferous 

 marls at Fort Dodge correspond to the upper faunal zone of the 

 Pella beds of southeastern Iowa as brought out by Weller and 

 Van Tuyl on pages 246 and 247 of the article mentioned above. 

 Their lower zone, characterized by ten or more genera of mol- 

 luscs, is apparently wanting in the beds representing the north- 

 ward extension of the Pella seas, at least in the Lizard creek re- 

 gion. 



The fossils are beautifully preserved and their most delicate 

 markings may be readily seen with a good hand lens. Freezing 

 and thawing and other agents of weathering have broken and 

 cracked many of the shells which lie exposed at the surface. Dis- 

 articulated valves of the larger species are not uncommon. 



"Jour. Geol., vol. XVII, p. 278, 1909. 



"Geol. Furv. III., Monog. I, p. 341, 1914, also explanation plate XLV. 



"Loc. cit. 



