466 A. W. GRABATJ PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



about 75 or 70°, thus making the contact, if the dip does not change, a 

 rectangular one. After the covered interval about 10 feet of red sand- 

 stones appear, somewhat conglomeratic. Then follows a coarse conglom- 

 erate or pudding stone, 5 feet thick and composed of a great variety of 

 pebbles. Again a shale bed occurs and then a conglomerate, with red 

 shale pebbles. Above this comes a thickness of about 120 feet of white 

 quartzite, some of the beds being marked by Artlirophycus harlani and 

 others by trails, mud Hows, and so forth. Pebbles are not uncommon in 

 some of the beds and clay galls abound in others, while toward the top 

 occur again some red beds. Conglomerate beds are found at frequent 

 intervals. The whole is succeeded by the Clinton, which here also con- 

 tains much red material, and this is followed by the Salina red shales. 

 These conditions can be traced northeastward to Swatara Gap. 



Throughout Pennsylvania the Tuscarora has in general the same dis- 

 tribution as the underlying red beds. These red beds, as repeatedly 

 noted, are not throughout of the same age, but in many sections a hiatus 

 and disconformity occur some distance below the top, the beds above this 

 hiatus being of Siluric or Medina age and those below of Ordovicic or 

 Queenston age. The disconformity is not recognizable in the sections, 

 but careful search might reveal the evidence for it. The deposition of 

 the reworked material, derived from the eastern extension of the older 

 beds directly on the western part of these same beds, would give very 

 little indication of a break, especially as the top beds of the older series 

 were probably reworked to some extent before the later' beds were de- 

 posited. Furthermore, the existence of such a hiatus would be obscured 

 by the presence of numerous smaller breaks in the series, such as are 

 characteristic of river-laid deposits. It may be that the new series begins* 

 in most cases with coarser beds, since the material is derived from the 

 coarser eastward extensions. But even this criterion may fail in some 

 cases. Of course, if characteristic Siluric fossils were present in the 

 upper beds, the Siluric age of the beds could then be proven, just as late 

 Ordovicic fossils in the lower beds prove their Ordovicic age. Here the 

 Artlirophycus harlani may be used, since so far as known this does not 

 occur below the Siluric. The Scolitlius verticalis is also serviceable to 

 some extent, though of much less importance. 



The thickness of the Medina portion of the Juniata is consequently 

 not known, but I doubt if it is much over 100 feet in most of the section, 

 and in some it is probably much less, though an occasional greater mass 

 may easily be found. On the whole these deposits are restricted to the 

 more westerly outcrops, the Tuscarora resting more often on the Juniata 

 in the east. 



