EXTENT OF FOLDING AND SUBSEQUENT EROSION 457 



Tuscarora of Pennsylvania, and a lower, softer, thinner-bedded, red or 

 brown sandstone and quartzite which merges into the sandy beds of the 

 Martinsburg below. How much of these red beds belongs to the Ordo- 

 vicic and how much to the Siluric (Medina) has not been ascertained. 

 The fact that the red series varies considerably in thickness might indi- 

 cate that most of it is Siluric (Medina), while the fact that the beds 

 grade down into the Martinsburg would indicate that the lower part is 

 Ordovicic, with a hiatus between it and the upper portion. A few im- 

 pressions of shells have been recorded from dark shaly beds about 200 

 feet above the Martinsburg, but no determination of species seems to have 

 been made. We have thus apparently a continuous succession of Upper 

 Ordovicic strata for a distance of 350 or 400 miles from southwest to 

 northeast. From the fact that the formation disappears abruptly south 

 of its thickest development, it would seem that it may have extended for 

 at least 100 miles more to the southwest. The linear extent of the north- 

 west and southeast outcrop is less than 90 miles, but, when the extensive 

 folding and faulting is taken into consideration, it will be found that it 

 was originally at least twice that. The easternmost outcrop of these beds 

 is now removed about 50 miles from the old land which could have sup- 

 plied the material. Doubling this on account of folding and thrusting — 

 here probably occurring at least twice — and we get a total extent of at 

 least 300 miles northwest and southeast for the former extent of these 

 beds. The probabilities are that it was nearly 400 miles. Whether this 

 represented one delta or several confluent ones can not now be deter- 

 mined. Considering the northeast-southwest extent, the probabilities are 

 that these beds represent several confluent members. 



The thickness of the present beds gives us no clue to the thickness of 

 the beds at their maximum, even if it were possible to separate the Ordo- 

 vicic from the Siluric part, for extensive erosion has affected this area as 

 it affected the region of the Juniata fan. The eroded material here as 

 there was redepositecl as continental or seashore Medina sand, a deposit 

 probably present in greater or less thickness in most of the sections of 

 the southern Appalachians, especially the western ones. A part of the 

 eroded material was also redeposited as the Rockwood sands, which is 

 thickest and coarsest where 1 the Bays has been entirely removed by early 

 Siluric erosion. 



The question may now he asked, Was there any deposit corresponding 

 to the Bald Eagle farther north ? 1 1' it is true, as I believe it is ami hope 

 to show presently, that the Tuscarora quartzite is derived Prom the ero- 

 sion and redeposition of the eastern extension of the older Bald Eagle 



