NORTHERN SECTIONS APPALACHIAN REGION 407 



striking characteristics, challenge attention, and especially those with 

 which I am personally best acquainted by prolonged field and laboratory 

 study. I have elsewhere 7 outlined my views regarding a number of 

 American Paleozoic formations, the characters of which stamp them as 

 continental rather than marine deposits. Many of these are to be con- 

 sidered in the light of fossil deltas, and of these a few from the Ordovicic 

 and Siluric will 'be chosen as illustrations of ancient delta deposits. 



In the Appalachian Mountain region occur a number of conglomerates 

 and sandstones belonging in part to the Ordovicic and in part to the 

 Siluric systems, which by their characters show that they were deposited 

 as deltas partly marginal, with both subaerial and submarine portions, 

 and partly as purely subaerial or dry delta fans. 



These sandstones and conglomerates were originally assigned to a uni- 

 form horizon, and correlated with similar deposits of New York which 

 lie near the base of the Siluric. Two areas of such deposits can be dis- 

 tinguished : a northern, comprising Pennsylvania, New Jersey, and New 

 York, with the centers for the most part in Pennsylvania, and a southern 

 one centering in eastern Tennessee. 



THE NORTHERN SECTION 



The beds of this section form the bold monoclinal ridges of Pennsyl- 

 vania, extending southward into Maryland and northward through New 

 Jersey into the Helderbergs of eastern New York. In general, white 

 conglomerates and sandstones have been found to rest either conformably 

 or unconformably on the complex series of shales and sandstones known 

 collectively as the Hudson River group, the age of which has generally 

 been regarded as terminating with Lorraine deposits. The white con- 

 glomerates were formerly always identified with the Oneida conglomerate 

 of New York, which nearly all geologists, following TTall, placed below 

 the Medina, though Vanuxem distinctly assigned it its proper place at 

 the top of the red series. In central and western New York a lower 

 quartzite, the Oswego, which lies below the Medina as currently defined, 

 was correlated with the Oneida, as was also the Shawarigunk of (he ITel- 

 derberg region. 



In most localities a red shale and sandstone often of great thickness 

 was found above the lower conglomerate, or, where the latter was missing, 

 rested directly on the Hudson River beds. This was identified with the 

 Medina red beds of New York. In Pennsylvania a second white con- 



7 A. w. Orabau : Continental formations in the North American Paleozoic. Compte 

 Rendu du Xle Congres Geologique international, Stockholm, L01O, pp. 097-1003. 1913, 



