112 STUART WELLER 



horizon, is scarcely or not at all recognizable beyond a short distance 

 south of St. Louis. The fauna of these shaly Warsaw beds is more or 

 less closely allied to that of the subjacent formations, but it contains 

 numerous species which are quite distinct and some which are either 

 identical with, or related to, members of the superjacent faunas. 



Subsequent to the Warsaw sedimentation the land to the north of 

 the Mississippi Valley Basin was elevated. The Salem limestone 

 which lies immediately above the Warsaw has a thickness of onlv 8 or 

 lo feet at Warsaw, 111.,' where the formation consists of an impure, 

 arenaceous limestone. To the south it increases in thickness to a 

 maximum of about loo feet, and is for the most part a very pure 

 limestone, although magnesian layers are not unusual. The forma- 

 tion extends eastward beneath the younger formations, and is again 

 exposed in western Indiana, off the western shore of the old Cincinnati 

 island. A notable feature of the formation is the presence in it, 

 throughout its entire geographical extent, of more or less extensive 

 oolitic beds. 



The fauna of the Salem limestone, commonly known as the Spergen 

 Hill fauna, contains many diminutive forms, one of the most common 

 species being Cliothyris hirsuta, which was present in a Kinderhook 

 oolite at Burlington, la. Several small forms of Conocardium are also 

 common in the fauna, one of the species, C. meekana, being somewhat 

 closely allied to C. pulchellum from the same Kinderhook oolite. A 

 comparison of the fauna with the Mississippian faunas of other parts 

 of North America indicates a close relationship with certain faunas far 

 to the northwest in Montana and Idaho. Meek^ has recorded a fauna 

 from a limestone in Idaho in which nearly one-half of the forms are 

 identical with Spergen Hill species, and in the Yakinikak limestone^ in 

 northwestern Montana a similar fauna also occurs. These limestones 

 in Montana and Idaho are doubtless to be associated with the Madison 

 limestone of the Yellowstone National Park, in which occurs a fauna 

 having relationships with the Kinderhook of the Mississippi Valley, 

 and especially with that of the Kinderhook oolite bed at Burlington, 

 la., a relationship which may account for the partial recurrence in 



1 ///. Slate Geol. Surv., Bull. No. 8, p. 90. 



2 Am. Jour. Sci. (3), V, 383. 



3 Bull. Geol. Soc. Am., XIII, 324. 



