428 A. W. GRABAU PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



(Pulaski), is more than twice as thick as the Frankfort and Pulaski of 

 New York. It seems more than likely that the Oswego sandstone of the, 

 south shore of Lake Ontario was also deposited during Upper Lorraine 

 time, and is to be included with the Pulaski and Frankfort beds in that 

 division. Northward in the Quebec region, as we have seen, this sand- 

 stone is absent and the Upper Hudson beds are of Eichmondian age. 



The influence of the currents bringing the quartz sands of the Oswego 

 was evidently not felt in the Quebec region, where continuous deposition 

 went forward. From this fact, and the general character of the beds in 

 the Saint Lawrence, it is safe to argue that the Adirondack old land was 

 not exposed, but covered to a greater or less degree by the Lorraine- L T tica 

 strata, as well as the Trenton limestones beneath these. The abundant 

 fragments of Trenton and Beekmantown limestone scattered over parts 

 of the region further indicate the former presence of a covering of these 

 rocks. 42 



Summary history of the Bald Eagle delta. — If we now correlate all the 

 facts so far ascertained with reference to the closing deposits of the Ordo- 

 vicic in eastern North America, we find that the Bald Eagle conglom- 

 erate of central Pennsylvania is best explained as a coarse pebble and 

 sand delta of subaerial origin, built by a large stream from the old land 

 to the southeast into the Upper Ordovicic Sea which covered the present 

 Appalachian region. The debouchure of this stream was in the neighbor- 

 hood of Tyrone, Pennsylvania, as shown by the great thickness of the 

 deposits there. The upstream continuation of this delta has partly been 

 removed by erosion and in part it is concealed by faulting. The delta was 

 perfectly conformable with the underlying Hudson strata of earlier age, 

 and represents merely the local accumulation of coarse river sediment 

 brought by a revived stream from the rising highlands on the southeast. 

 Other similar streams no doubt existed and their deposits gave rise to the 

 coarser beds occasionally found in the Upper Hudson series, but none 

 seem to have been so pronounced. My belief is that this delta-building 

 commenced in Upper Eden (Frankfort) time and continued through 

 Lorraine or until the Pulaski shales and Oswego sandstone were de- 

 posited. The latter, indeed, must represent the upper part of the Bald 

 Eagle, the most extensive (areally) of the overlapping beds of the series. 

 The close of the building of this delta probably fell in late Maysville 

 time, but before the end of that epoch. In the east the end of the Mays- 

 ville epoch was inaugurated by red sedimentation, which continued 



42 See Ida H. Ogilvie : Paradox Lake quadrangle. Bull. 96, N. Y. State Museum, p. 

 467. This is also held by Cushing. (See N. Y. State Museum Little Falls Bulletin.) 



