502 GEOLOGY. 



The rich deposits of zinc and lead ore in southwestern Missouri and 

 eastern Kansas are chiefly in the Osage (Burlington) beds/ though the 

 metallic materials were concentrated into ores at a much later time. 



During the second or Osage stage of the Mississippi basin the con- 

 ditions of sedimentation in Michigan seem to have remained much as 

 in the Kinderhook stage, and the accumulation of clastic sediments 

 continued. 



East of the Cincinnati arch, which probably remained above water 

 as an island, the deposition of clastic sediments was also continued, 

 the sediments of eastern Ohio constituting a part of the Waverly 

 series. 2 Still farther east, the accumulation of the sand and gravel 

 of the first stage (Pocono) either continued, or had been succeeded 

 by the deposition of the mud which now constitutes the Mauch Chunk 

 shales. 3 The exact time-relation of these shales to the Osage epoch 

 is undetermined. 



While the Mauch Chunk shales succeed the Pocono sandstone of 

 eastern Pennsylvania, with no intervening formation, there is, in western 

 Pennsylvania, a lentil of limestone in the shales. To the south, this 

 limestone thickens at the expense of the shale, and in Maryland 4 and 

 Virginia constitutes a well-defined formation of limestone (Greenbrier) 

 lying between the Pocono below and the Mauch Chunk above. The 

 Newman limestone of more southerly regions 5 is perhaps the equiva- 

 ent of the Greenbrier, or of the Greenbrier and Pocono. 



The St. Louis formation. — During the third recognized stage of 

 the period, limestone (St. Louis) deposition was continued in the 

 Mississippi basin, but the fauna which it contains is so unlike that 

 which had preceded as to show that geographic changes of consequence 

 to the marine life of the interior had taken place. The changes seem 

 to have been connected with the removal of a barrier somewhere in 

 the west, which allowed the fauna of the Great Basin region, hereto- 

 fore shut off from that of the interior, to migrate eastward, and minge 

 with that of the Mississippi basin. This stage marks the time of 

 maximum Mississippian submergence, so far as the western interior is 

 concerned (Fig. 228). 



1 Bain, Van Hise, and Adams, 22d Ann. Rept., U. S. Geol. Surv., Pt. III. 



2 In addition to the State Reports of Ohio, see Prosser, Jour, of Geol., Vol. IX, 

 pp. 205-31, and Vol. XI, p. 519. 



3 Probably of terrestrial origin. Barrell, G. S. A., Dec., 1906. 



4 Prosser. Jour, of Geol., Vol. IX, p. 422. 5 See Tennessee folios. 



