m 



A. W. G&ABAU TYPES OF SEDIMENTARY OVERLAP 



the eastern outcrops in Pennsylvania has been accepted as the equivalent of 

 that in the western counties, as though the westward decrease were due merely 

 to lessened thickness in each of the subdivisions. It must be clear, however, 

 . . . that the loss in thickness is due very largely to disappearance of the 

 lower members of the section, as is the case also southward from central 

 Kentucky and southern Virginia, so that in Alabama and much of Tennessee 

 only the uppermost beds remain. A new correlation appears to be necessary."* 



The general change in the character of the sediments from conglom- 

 erates and coarse sandstones in the east to shales in the west is also 

 emphasized by Stevenson. The relationships of these deposits may be 

 expressed in the following diagram: 





^rsn 







Figure 14. — Relation of Waverley and Chemung Formations to the Pocono and Catskill. 



The Mauch Chunk. — The Mauch Chunk period of Appalachian history 

 seems to have been a period of more stationary conditions, accompanied by 

 some subsidence, as shown by the fact that fine sediments characterize 

 the formation throughout, and also by the presence of extensive marine 

 limestones. In the northern Appalachians heavy non-marine sediments 

 still accumulated.. Thus in the type region 2,168 feet of red shales, with 

 some sandstones in the upper part, constitute this formation. A little 

 north of Mauch Chunk, Pennsylvania, the formation of this name has a 

 thickness of 3,342 feet and consists almost wholly of red shales. 



In the Broad Top region of Huntingdon county, Pennsylvania, the 

 basal part of the Mauch Chunk consists of 141 feet of shales and sand- 

 stones, followed by 49 feet of limestone (Greenbrier), and this by 910 

 feet of sandstones and shales. In northeastern Lycoming county, 30 

 miles from Mauch Chunk, the base of the formation consists of 120 feet 

 of shales, followed by 75 feet of marine limestone and 150 feet of shales. 

 In northwestern Lycoming county the basal beds have been reduced to 

 80 feet, while the upper beds are only 20 feet thick, the intervening lime- 

 stone measuring 50 feet. In Potter and in McKean counties only the 

 upper beds are present, decreasing from 70 feet in the first to 50 feet in 

 the second, and finally dying away westward as a coaly black shale. 



Southward from the type region of non-marine sedimentation the 

 marine phase thickens. Thus on the Potomac, in the Maryland Alle- 



