STRATIGRAPHIC TAXONOMY 629 



clature when Hershey several years later proposed "Ozarkian" for a post- 

 Pliocene period of erosion. 



Broadhead's Ozark series, as described by him, embraced all the beds 

 in the Ozark uplift in Missouri between the pre-Cambrian complex in the 

 Saint Francois Mountains and the top of the Joachim limestone (First 

 Magnesian limestone of Swallow). Like Swallow before him, he be- 

 lieved the base of the "Fourth Magnesian limestone" to be, if anything, 

 a little older than the Lamotte sandstone. Eecent investigations prove 

 this opinion in error, but it is unnecessary to point out the details. It 

 will suffice to state that Swallow's Fourth Magnesian is younger than the 

 Potosi dolomite — which constitutes the base of the Ozarkian system in 

 Missouri — and of course younger than the Elvins, Bonneterre, and La- 

 motte, which together constitute the upper Cambrian as developed on the 

 flanks of the Saint Francois Mountains. Broadhead's definition of the 

 Ozark series is further modified by elimination of the two upper mem- 

 bers — the "First Magnesian" and the Saint Peter sandstone — which be- 

 long at the base of the second system above the Ozarkian, namely, to the 

 Ordovician. Broadhead did hot know that a great system of rocks is 

 developed in the Appalachian region — indeed, it is scantily represented 

 even in southern Missouri and better in the adjoining State of Arkan- 

 sas — between the Saint Peter and the Jefferson City dolomite ("Second 

 Magnesian limestone"). In Missouri, then, the Ozarkian comprises all 

 beds younger than the Elvins and older than the base of the Canadian 

 system represented in north Arkansas by the Yellville dolomite. 



A detailed description of the Ozarkian formations in Missouri will not 

 be attempted here. Preliminary descriptions were published by Bain and 

 Ulrich,^*^ and more recently by Buckley.^'^ The latter makes such addi- 

 tions to the section and changes in nomenclature as had become desirable 

 in the meantime. The sequence and grouping of the Eopaleozoic forma- 

 tions given by Buckley (op. cit., pages 15, 19) is essentially as in my 

 correlation table, except that he draws the Cambro- Ozarkian boundary at 

 the top of the "Central Marble bed," while I have finally decided that it 

 should be drawn at the important unconformity between the Elvins and 

 the Potosi. 



A full description of the formations, faunas, and geologic history of 

 the Ozark uplift being in course of preparation, the following brief notes 

 on the formations of the typical Ozarkian section may be sufficient for 

 present purposes. 



«» BuH. U. S. Geological Survey, No. 267, 1905, pp. 26-35. 



8T Missouri Bureau Geology and Mines, vol. ix, pt. 1, 1009, pp. 51-62. 



