DISCUSSION OP TYPICAL ILLUSTRATIONS 143 



similarity in the sequence of sediments * can be clearly recognized be- 

 tween the sections of Maryland and Virginia and those in the New York 

 and Pennsylvania area of the Devonian. 



If lines are drawn across the sections in New York state corresponding 

 to the more strongly marked lines of separation between different types 

 of this sedimentation, they serve to divide off a set of standard forma- 

 tions, and the fossils of these formations have been tabulated to consti- 

 tute the faunas of the formations so established. Thus the Corniferous, 

 Marcellus, Hamilton, etcetera, are established as standard formations. 

 Passing a few hundred miles to the southward, to Virginia, similar lines 

 may be drawn across the same general series of Devonian sediments to 

 make three divisions corresponding in a general way with the more 

 striking divisions of the New York section ; but they do not agree in 

 detail, in thickness, or in fossil contents. While, therefore, it may be 

 convenient to speak of them as occupying the same general place in 

 stratigraphic succession with the New York formations indicated as cor- 

 related with them, the differences in all of their visible characters are 

 sufficient to forbid calling them the same formations, or even chrono- 

 logic equivalents. 



ANALYSIS OF THE FAUNAS 



The analysis of the faunules, as gathered in Bulletin 244, shows that 

 the fossil faunas contained in the strata classified in the folios as Rom- 

 ney, Jennings, and Hampshire are not the same as those of the New 

 York formations with which they are compared, namely, the rocks be- 

 longing to the part of the column called Romney, in central and southern 

 Virginia, contain chiefly the faunas found in New York in the Marcel- 

 lus, Genesee, and Nunda (" Portage"), with only traces of the Hamilton 

 fauna near their base. The Jennings formation does, in many cases, 

 hold a " Chemung fauna; " but as it is followed southward along the 

 Appalachian this latter fauna is lacking, and the succession is then di- 

 rectly from the black Romney shales upward into a Mississippian, or 

 lower Carboniferous, fauna, occurring in the shales after the black shale 

 sediments ceased, while the fauna of the Genesee- Portage formations of 

 New York chiefly fills the lower interval. The evidence indicates that 

 when the specific Hamilton, Ithaca, and Chemung faunas are wanting in 

 the sediments of the middle Appalachian region a fauna of the type 

 (found intercalated between them in the New York area) seen in the 

 Marcellus, Genesee, and Nunda (" Portage ") of New York, dominates 



♦Passing from limestone through black shales, fine and evenly laminated; then coarser, thin 

 bedded, argillaceous shales and sandstones ; next sandstones of thicker and more frequent occur- 

 rence, running into coarser cross-bedded sandstone with red beds occasionally interspersed, and 

 finally coarser sandstones with occasional conglomerates. 



