CONTENTS. xxill 



PAGE 



The decline of the crinoids, 530. The culmination 

 of the Mastoids, 530. Partial recovery of the corals, 

 530. New devices of the bryozoans, 531. The pro- 

 tozoans make a record, 531. Changes in the brachio- 

 pods, 531 . The mollusks, 533. Other forms, 533. The 

 evolution of the fishes, 534. 

 II. The Land Life of the Mississippian 537 



CHAPTER X. 



THE PENNSYLVANIAN (COAL MEASURES, CARBONIFEROUS PROPER) 



PERIOD. 



Formations and Physical History : . . . 539 



The Pottsville Conglomerate (Millstone Grit) ' 539 



The Coal Measures 541 



Distribution and Outcrops 542 



Productive Coal-fields 546 



The Anthracite field, 546. The Appalachian field, 

 546. The Northern Interior field, 548. The Eastern 

 Interior field, 548. The Western Interior and South- 

 western fields, 548. The Nova Scotian-New Brunswick 

 coal-field, 548. East of the Appalachians, 549. West 

 of the Great Plains, 549 



Sections of the Mississippian and Pennsylvanian Systems 556 



Section in northern Pennsylvania, 557. Section in 

 southwestern Pennsylvania, 557. Generalized section 

 for West Virginia, 558. Section in western Virginia, 559. 

 Section in southern West Virginia and western Virginia, 

 559. Section in east-central Kentucky, 560. Section 

 for Ohio, 560. Section in northern Missouri, 561. Sec- 

 tion in Arkansas, 562. Section in northern Texas, 563. 

 Section in west-central Colorado, 563. 



The Coal _-. . r 564 



Origin, 564. The history of a coal-bed, 571. Extent 

 and relation of coal beds, 574. Varieties of coal, 576. 



Iron Ore 580 



General Geographic Conditions in the Eastern Interior 581 



Thickness 582 



Duration of the Coal-Measures Period 583 



