PENNSYLVANIA AND DEPOSITS THEREIN. 53 



are long ridges of foreset-bedded gravels with infrequent cobbles 

 and boulders, which extend towards the Delaware from the low hills 

 or the projecting shoulders of South Mountain, which formed long 

 areas of diminishing slackness. The bars thus diminish both in 

 height and breadth as they near their ends. The lodging of bergs 

 nearby made changes in the strength of the scour, and we find sur- 

 faces of erosion with unconformable beds on either side. This is 

 especially the case at the end of the period when fine gravel was de- 

 posited, and the Packer Clay with its boulders and iceberg trash fol- 

 lowed as a capping. Some of these bergs carried masses of rock 

 weighing four and one half tons, and a heap of such masses were 

 found on top of an eddy hill in what was South Bethlehem. 



This clay capping is sandy and but 2 feet thick near lines of cur- 

 rent of 5 inches per second ; but is 30 feet thick and sand-poor in 

 areas of still water. It lies unconformably over the ends of some of 

 these long bars, and proves that their sculpturing preceded its depo- 

 sition, and that they were never part of a complete valley filling since 

 excavated. This latter was the theory of J. P. Lesley in his intro- 

 duction, p. 37, to F. Prime's third report (D3, Second Geol. Surv. 

 Pa., 1878), where he characterizes the Bethlehem gravels as "a high- 

 flood river deposit, or an ancient high-level river-channel deposit." 



Susquehanna Ponding. 



This valley is so broad that the only places where damming took 

 place in the Kansan Border are at the narrows near Rupert and at 

 Little Mountain. The ice-dam in the former must have been above 

 160 feet high, as the Berwick upper sands reach that elevation, and 

 carry glaciated cobbles and boulders.* At Nescopeck, opposite Ber- 

 wick, E. H. Williams, Jr., reported* in 1895 • 



There are three formations in the gravels at Berwick and Nescopeck: 

 first, subglacial till so compact that a pick can scarcely be driven into it. This 

 has a clay base and carries an abundance of rdlled stones of all the formations 

 to the north — even granite and anthracite meet in the mass. On this is a 

 bed of modified drift of loose nature and sandy matrix with the same collec- 

 tion of rolled stones, and of equal freshness. In fact there is no difference in 

 the color of the layers. . . . The lower inch of the gravels is a conglomerate 

 with a limonite matrix, where the percolating waters laden with the solution 

 of iron were stopped by the dense till below. Capping all is a layer of un- 

 stratified sand that varies in thickness greatly within a few feet, and carries 

 streaks of gravel, glaciated cobbles and boulders at all levels. 



