STE. GENEVIEVE MARLS NEAR FORT DODGE 603 



Geology of the Des Moines Valley, writes of the rocks "along the 

 bed of Lizard fork, . . . . " aiid adds that "the marl bed above con- 

 tains three or fonr species of Terebratnla, a Spirifer, and the 

 tail of a trilobite. " His specievs of "Terebratnla" are no doubt 

 the forms we now know as Pugnoides oUumica, Composita tri- 

 nuclea, and Girtyella indianensis; his "Spirifer" is S. pellaen- 

 sis. The Spirifer is the only member of the fanna ilhistrated and 

 described by Hall in the paleontological part of the report just 

 mentioned. 



In 1870, Wliite^ in discussing- the St. Louis limestone says that 

 "the following- species are regarded as more characteristic of the 

 formation than any others: Spirifer keokuk var. (Hall), Rhyn- 

 chonella otUimwm (White), Athyris amhigua (Sowerby) ...... 



the three are as common at Fort Dodge as they are in 



the southeastern part of the state, although the two points are 

 two hundred miles apart. ' ' These three species are the same as 

 the "Spirifer" and two of the "species of Terebratnla" men^ 

 tioned by Worthen. 



Wilder" in the Webster county report says that "this marl is 

 extremely rich in fossils" and he lists the three commonest bra- 

 chiopods and "Dentalium sp." It is not clear what fossil Doc- 

 tor Wilder designated as Dentalium, — careful collecting has not 

 yielded a single specimen of this genus of pteropods. 



Both White and Wilder followed HalP in assigning the fanna 

 of the marl to the St. Louis limestone. In a recent article in the 

 Proceeding's of this Academy Weller and Van TuyP bring out 

 the fact that geologists working in southeastern Iowa had shown . 

 years ago that the upper part of the St. Louis limestone, as then 

 delimited, differed f aunally and in many cases lithologically from 

 the greater mass of the formation below. To this upper part 

 Bain^° gave the name Pella beds because of its typical develop- 

 ment at the town of Pella in Marion county ; he still regarded the 

 beds as a distinct unit of the St. Louis. In 1890, Ulrich^^ de- 

 scribed some bryozoan fossils from the Pella beds at Pella and 

 in the same year Nickles and Bassler^- referred the beds to the 

 Ste. Genevieve formation on the basis of Ulrich's bryozoa. Later 



oRept. on the Geol. Surv. Iowa, vol. I, pp. 221, 222, 1870 



■Iowa Geol. Surv., vol. XII, p. 78, 1901. 



«Geol. Surv. Iowa, vol. I, pt. II, p. 677, 1858. 



»Loc. cit. 



i»Iowa Geol. Surv., vol. IV, p. 282, 1894. 



"Geol. Surv. 111., vol. VIII, pt. ii, pp. 434, 448, 449. 



i=U. S. Geol. Surv., Bull. No. 173, pp. 166, 180. 



