24 FLUORSPAK DP:P0SITS of southern ILLINOIS, [bull. 255. 



TRIBUNE LIMESTONE. 



Character mid relations. — At the Fairview mine the foot wall of 

 the vein at the surface consists of a coarse, crystalline, nonmagnesian 

 limestone, light gray to white in color and containing minor quanti- 

 ties of oolite and of chert. The following fossils were collected from 

 it and recognized by Mr. Ulrich : 



Zaphrentis spimilifera. Zeacrinus manniformis. 



Pentreiuites godonii. Lyropora rana. 



Pentreinites pyriformis. Lyropora subquaclrata. 



Pentremites tubereulata. Spirifei- iiierebescens. 



Steiiopora cervinus. Spirifer leidyi. 



On the basis of these fossils he determined this limestone to be the 

 same as that at Tribune, Ky., representing the middle Chester. It 

 is impossible at Fairview to determine much regarding the relations 

 of the limestone. It is cut off on all sides by faults, and its thickness 

 is somewhat uncertain. The shaft at a depth of 200 feet show^s simi- 

 lar limestone on the foot wall. Whether it is indeed the same or 

 represents the Ste. Genevieve can not be positively ascertained, since 

 it is impossible to make a complete examination of the wall rock from 

 the top to the bottom of the shaft. At the first or 30- foot level Filers 

 mentions calcareous shale, and at the same level disintegrated sandy 

 material may now be observed. This may possibly represent the 

 Cypress sandstone, and. if so, the Tribune would here have a thick- 

 ness of less than 50 feet. The Tribune limestone has not been defi- 

 nitely recognized at any other point in the tw^o counties, though 

 there are at a number of points thick limestones which may possibly 

 represent it. At none of them, however, were the fossils found which 

 are considered to be peculiarly characteristic of it. 



RIRDSVILLE FORMATION. 



Character. — This formation includes sandstones, shales, and lime- 

 stones. In distinction from the Cypress sandstone below and the 

 Mansfield above, the Birdsville sandstones are particularly thin 

 bedded. They seldom show massive character, and do not, so far as 

 observed, give rise to sharp l)luft's and canyons. They frequently 

 grade into shales, becoming less and less sandy until true argil- 

 laceous shale is found. The latter is occasionally thin bedded, black, 

 and fissile, and contains thin coal beds. Interbedcled with the shale 

 and the sandstone are thin limestone beds. The latter are usually 

 somewhat argillaceous and are chert bearing. They are usually only 

 a few feet thick, though one body having a maximum of 50 feet 

 occurs in the formation. 



The general impression of the formation as a whole which one 

 gains from traveling over it is that it is mainly a sandstone. It may 



