THE STE. GENEVIEVE MARLS NEAR FORT DODGE 

 AND THEIR FAUNA.^ 



JAMES H. LEES AND A. 0. THOMAS. 



A. The Strata: — In his report on the geology of ^A^ebster 

 county- F. A. Wilder mentions the presence of a shaly marl rich 

 in fossils, which he includes with the St. Louis limestone. The 

 writers have had the opportunity of examining a number of out- 

 crops of these shaly marls and a study of the fossils collected 

 from them has •con-oborated the conclusion reached, apparently 

 somewhat tentativel.y, by Weller and Van Tuyl,^ that they are 

 Ste. Genevieve in age. Because of this cletermniation it seems 

 worth while to call attention to the character and distribution 

 of these beds and to their contained fossils. ]VIr. Thomas has 

 studied the fossil content of the beds while Mr. Lees, accompa- 

 nied to some of the exposures by Mr. Thomas, has examined the 

 different localities where the beds are known to outcrop. With 

 one exception all the outcrops here reported are located within 

 the valley of Lizard ereek, west of Fort Dodge.* This exceptional 

 locality is in a ravine which opens into Des ]Mk)ines valley from 

 the northwest opposite the dam and about one-third mile above 

 the railroad and wagon bridges over the river at the mouth of 

 Lizard creek. The streamlet has cut through the drift, which 

 is rather thin, through the Coal IMeasures, which are twenty feet 

 or more in thickness, and into the marly beds of the Ste. Genet- 

 vieve, to a depth of twenty to twenty-five feet. Owing to the uiv 

 consolidated nature of most of the beds some ■;f the exposures are 

 somewhat slumped. The Ste. Genevieve becl:; are exposed for 

 two hundred yards or more along the lower part of the ravine. 

 Just above the mouth of the ravine, the exposure shows two to 

 three feet of a dark red clay, which is overlain by twelve to fif- 

 teen inches of a gi'eenish gray clay. Above this lies a streak of 

 rather hard yellow to gi'ay shale, which, a hundred yards up- 

 stream, forms an eighteen inch ledge, which makes a small wa- 

 terfall in the stream. This ledge is in turn overlain by a light 

 gray shale with a yellowish tinge, which has a thickness of about 

 seven feet. This shale is richly fossiliferous, especially in certain 

 streaks, and is the only bed in which any fossils were found. 

 Above it lies a red clay shale having a maximum thickness of ten 



^Published with permission of tlie Director of the Iowa Geological Survey 

 2Iowa Geol. Sui-vev, Vol. XII. pp. 78-83. 1901. 

 nowa Acad. Science Vol. XXII. pp. 241-247. 1915. 

 *For additional localities see addendum at end of this paper. 



