400 STUART WELLER 



except that the freshly broken rock is commonly darker in color, 

 in some places nearly black, and it is associated with a greater 

 amount of shale, one of the most calcareous shale beds at the base 

 of the formation being highly fossiliferous. Near or perhaps at 

 the very base of this limestone in the southern counties, a thin 

 seam of impure coal, not more than two or three inches thick, has 

 been observed in a number of localities and is perhaps a persistent 

 band. A small amount of chert is present in the Menard, by no 

 means so great a quantity as in the Vienna, but distinctly more 

 than is commonly present in the Middle Chester limestones. 



The fauna of the Menard possesses many characteristics 

 common to the Chester formations generally, but certain other 

 features differentiate it quite sharply from those of the earlier 

 limestones of the series. The species of the two genera Spirifer 

 and Composita show a notable change in the Menard faunas from 

 the earlier forms, in being larger and more robust in form. The 

 typical examples of Spirifer increhescens are, initiated in this 

 horizon, and the typical Composita subquadrata takes the place of 

 Composita trinudea, which ' was the usual form in the older Hme- 

 stones. A very characteristic member of the fauna is the pelecypod 

 Sulcatopinna missouriensis, which occurs in most Menard col- 

 lections; in places it is very abundant, commonly standing verti- 

 cally in the limestone strata, probably the position it occupied 

 when Hving. This species occurs also in the Vienna Hmestone, 

 but more rarely than in the Menard, where it is associated with 

 the bryozoan Prismopora serrulata, which is unknown in the 

 Menard. The most fossiliferous horizon in the Menard is the 

 basal calcareous shale which is present in the southern counties, and 

 which has been recognized across Hardin, Pope, Johnson, and 

 Union counties. This bed is similar in character, both lithologic 

 and faunal, irrespective of whether the underlying Waltersburg 

 sandstone is thick, thin, or absent from the section. Among other 

 forms which are commonly met with in this basal horizon is the 

 blastoid Pentremites fohsi, and in the experience of the writer this 

 species has been found in no other horizon. 



The thickness of the Menard limestone in the Mississippi 

 River counties commonly varies between sixty and eighty feet, 



