362 0. F. Beecher — Cambrian Fossils of Missouri. 



Aet. XXXVIII. — Note on the Cambrian Fossils of St. 

 Frangois County, Missouri ; by C. E. Beechee. 



The small collection of fossils submitted to the writer by 

 F. L. Nason, for identification, is interesting, especially as it 

 determines the geological horizon of an extensive series of 

 limestones, sandstones, conglomerates, etc., in southeastern 

 Missouri, the age of which has hitherto been somewhat in 

 doubt. Also, since these strata are intimately associated 

 with the lead-bearing rocks of this region, the identification has 

 considerable economic value. 



It is stated by Arthur Winslow, in a paper on " The Dis- 

 seminated Lead Ores of Southeastern Missouri "* (p. 11), that 

 although these rocks are placed in the Lower Silurian " The 

 possibility still remains that there maybe afaunal break which 

 will admit of some of the lower strata being classed as Cam- 

 brian, though there is nothing in the stratigraphy to suggest 

 it. This must, therefore, be left to the paleontologists, and 

 owing to the dearth of fossils the problem is not an easy one 

 for them to solve." In Volume IX of the Missouri Geological 

 Survey (Pt. IV, p. 52, Keyes, 1895) the Fredericktown dolo- 

 mite (= St. Joseph limestone) is referred to the Upper Cam- 

 brian on account of the presence of Lingulella Lambomi 

 (Meek), but since this species is peculiar to the horizon, and 

 the genus has a much wider range, this correlation is not 

 established. A general statement is made by Keyes regarding 

 this region {I. c, p. 44) that " No strata younger than the Cam- 

 brian are believed to be represented. But few fossils have 

 been found in the rocks of the area, so that the faunal evidence 

 as to geological age is somewhat meager." The present collec- 

 tion of fossils, made by. Mr. Nason, indicates that the entire 

 series is older than the Lower Silurian (Ordovician) and that at 

 least the upper portion probably belongs to the Upper Cambrian. 



All but one species of the fossils were obtained from the 

 lower members of the Potosi limestones, and, since this is the 

 topmost formation of this region, its correlation is of the first 

 importance. The fossils occur abundantly in the limestone 

 and conglomerate beds and more sparsely in the sandstones. 

 They consist chiefly of fragments of trilobites, with a few 

 brachiopods and other forms. Lithologically there is a very 

 close resemblance between these fossil-bearing beds and those 

 of a similar horizon in the Black Hills of South Dakota. 

 Limestones, limestone-conglomerates, and sandstones of the 

 same appearance are found in both sections. Faunally, there 



* Bulletin No. 132 of the United States Geological Survey, 1896. 



