578 



COAL MEASURES OF MARYLAND 



SPECIES. 



Spharodoma fusiformis (Hall)? 



SphcBrodoma primogenia (Conrad) .... 

 SphcETodoma primogenia var. nov .... 



Spharodoma ventricosa (Hall) 



Zygopleura plicata (Whitfield) 



Zygopleura scitula (Meek and Wor- 



then) 



Zygopleura sp. nov 



Zygopleura sp. nov 



Aclisina stevensana (Meek and Wor- 



then) : . 



Holopea aflf. micula (Girty) 



MoLiyUSCA — Cephalopoda 



Orthoceras colletti Miller 



Pseudorthocerasknoxense (McChesney ) 

 Tainoceras occidentalis (Swallow) . . . . 



Metacoceras dubium Hyatt ? 



Metacoceras perelegans, var. nov 



Metacocaras sculptilis, var. nov 



Arthropod A — Trilobata 



Griffithides sangamonensis (Meek and 

 Worthen) 



Arthropod A — Branchiopoda 



Estheria ortoni Clarke 



MARY- 





PENNSYL 





WEST 



LAND. 







VANIA. 





VIRGINIA. 



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Part II. Correlatiox of the Coal Measures, by Charles Iv. 

 SwARTz^ W. Armstrong Price, and Harvey Bassler 



METHOD OF CORRELATIOX 



Criteria employed. — The correlation of the Coal Measures of Maryland 

 with those of other areas appears to have been based in large degree, in 

 the past, upon three assumptions, namely, the constancy of intervals 

 between coals, the persistence of coal strnctnres, and the persistence of 

 the lithological features of the strata, other than coals, over large areas. 

 That these assumptions are not trustworthy, when unsupported by pale- 

 ontological and other evidence, is readily seen when we compare th-~ 

 relative uniformity of marine sediments with the variability of conti- 

 nental deposits. 



