20 MISSISSIPPIAN BRACHIOPODA 



has been used for the formation, 1 but this name was also used much earlier 

 and is still in use for a formation in Ohio, which prior use makes it 

 unavailable for the formation here under consideration. In 1901 Cumings 2 

 proposed the name Salem limestone for the formation, and in 1904 

 Ulrich 3 used the name Spergen in exactly the same manner. Cumings' 

 name clearly has priority as a formation name, and by the application 

 of the "law of priority" his name must be adopted and is consequently 

 used here. 



This formation is represented in the section at Warsaw, Illinois, by a 

 bed of limestone about 8 feet in thickness. It increases to the south, 

 and from Jersey to Randolph counties, its thickness is from 100 to 160 

 feet. The formation is limestone, almost entirely free from chert through- 

 out, although the beds vary greatly in lithologic character. Some beds 

 are very pure, white limestone, in many places containing great numbers 

 of bryozoans ; some beds are oolitic, while others are decidedly dolomitic. 

 Many years ago one of the magnesian beds was mined in Jersey and St. 

 Clair counties for the manufacture of hydraulic cement. Towards the 

 summit of the formation some of the beds assume lithologic characters 

 resembling the superjacent St. Louis limestone, the transition from one 

 formation to the other being gradual, without a distinct stratigraphic 

 break. 



The fauna of the Salem limestone has long been known as the Spergen 

 Hill fauna, from which locality, in Indiana, it was long ago described by 

 Hall and later beautifully illustrated by Whitfield. The fauna contains a 

 large number of species, many of which are in many instances diminutive 

 in form. Brachiopods and fenestelloid bryozoans are among the most 

 conspicuous members of the fauna, in addition to which many gastropods 

 and pelecypods are locally present, besides some corals and other forms. 



St. Louis limestone. The St. Louis formation has its typical develop- 

 ment in St. Louis and in the Mississippi river bluffs to the north and south 

 of that city. It is essentially limestone throughout, in some places quite 

 free from chert, and in others with conspicuous chert beds, but nowhere 

 represented by such extensive chert beds as are commonly present in 

 the lower portion of the Osage group. The limestones of the formation 

 are more or less heavy-bedded, and vary considerably in lithologic texture, 

 but are rarely oolitic. A very characteristic phase is exhibited in beds 

 of compact bluish-gray limestone, very brittle and breaking with a conch- 

 oidal fracture, and generally exhibiting a texture almost like that of 

 lithographic stone. In the bluffs north of Alton the formation contains 



121st Ann. Rep. Dept. of Geol. and Natl. Resources, Indiana, pp. 291-427 (1897). 

 2 Jour. Geol., vol. 9, p. 232 (1901). 



3U. S. Geol. Survey, Prof. Paper, No. 24, p. 90 (1904); Mo 1 . Bureau Geol. and 

 Mines, vol. 2, 2nd ser., p. 110 (1904). 



