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FORMATIONS AND PHYSICAL HISTORY 427 







>ok) \VITI- partly calcareous. At the same time, the area of South- 

 mi M icliigan was a sort of bay or partly enclosed sea receiving sedi- 

 ment from surrounding lands. Most of these formations are marine, 

 but the Pocono has yielded fossils of land life. The formations of 

 this stage are less widespread than those of later stages. 



In the second (Osage or Augusta) stage of the period, the sea of 

 interior was clearer, and the deposition of limestone was general. 

 ni'iK-i- extended westward, probably to New Mexico on the 

 e hand and to Montana on the other. The rich deposits of zinc 

 (with some lead) in southwestern Missouri and eastern Kansas 

 are chiefly in the Osage beds, though the metallic compounds were 

 concentrated into ores at a later time. 



East of the Cincinnati arch, which was probably an island at this 

 ;e, the deposition of clastic sediments continued. Those of 

 stern Ohio constitute a part of the Waverly series. Farther east, 

 e accumulation of sand and gravel continued, or had been suc- 

 :eded by the deposition of the mud which constitutes the Mauch 

 C 'hunk formation. The sediments of at least a part of this formation 

 seem to have accumulated on land, rather than in the sea. In 

 Maryland and elsewhere farther south, a formation of limestone 

 (Greaibricr) lies between the Pocono and the Mauch Chunk. 



The St. Louis stage marks the time of maximum Mississippian 

 submergence, so far as the western interior is concerned (Fig. 374). 

 Limestone deposition continued in the Mississippi basin. It was 

 at this time that the Bedford limestone 1 of Indiana (Salem or 

 S 'per gen formation), famous as a building stone, was deposited. 

 Much of this limestone, long mistaken for oolite, is made up of the 

 shells of foraminifera. Many of the great limestone caves in Ken- 

 tucky and southern Indiana are in the limestone of this epoch. In 

 Muhigan, beds containing salt (brine) and gypsum were being laid 

 >\vn, as at certain earlier stages in the period. 



In the northern part of the Appalachians, the Mauch Chunk 

 ales were in process of deposition. Other names are applied to 

 e contemporaneous deposits in the mountains farther south, 

 ically, deposits of this time contain both coal and iron ore. 

 The Chester stage of the period was marked by more restricted 

 ters and more varied sedimentation. The deposits of this stage 

 .emble in a general way those of the Kinderhook stage. Those 



1 This name as applied to this limestone, is a trade name. As a geological 

 i, Bedford is applied to a member of the Waverly series farther east. 



