102 J. Barrett — Upper Devonian Delta of the 



age perhaps three to six inches in diameter but those up to 12 

 and 15 inches are common. Eight miles east of the Delaware 

 the writer has noted bowlders from 21 to 30 inches in diameter. 

 The quartzite bowlders of this locality are regarded by Wherry 

 as of Silurian origin. No careful lithological studies have been 

 made of those in New Jersey, however, to determine if they 

 were derived from the Silurian or Upper Devonian forma- 

 tions. 



The size and the degree of rounding of the quartzite con- 

 glomerates show that they have been carried by streams, but 

 probably in most cases from regions within five, ten or fifteen 

 miles. Many of the cobbles indicate distinctly less transporta- 

 tion than do the bowlders of the Upper Devonian con- 

 glomerates of New Jersey. Their volume, their persistence 

 through the Newark sediments and their coarseness in beds 

 high in the group show that they came from formations of 

 great volume which were progressively elevated. 



This discussion o'f the geology which existed during the 

 upper Triassic throws light upon the extent at that time of the 

 Paleozoic formations. What is now the Great Valley and 

 much of the Archean Highlands of Northern New Jersey was 

 mantled then by heavy formations of quartzite of which the 

 Green Pond axis is the sole isolated remnant. The thorough 

 cementation of this quartzite appears to show that at the end 

 of the Paleozoic it had been covered by still higher formations, 

 possibly by overthrust. The volume of quartzite in this 

 region in the upper Triassic implies an earlier extension still 

 farther eastward. 



In Pennsylvania south of latitude 10° 30', although nearer 

 to the present outcrops of the upper Paleozoic, such a Triassic 

 mantle of Paleozoic quartzite does not appear to have existed. 

 It is to be inferred that the Permian folding carried it here so 

 high that the early Triassic cycle of erosion pushed back the 

 outcrops to near the present line of vertical emergence. 



The Jurassic Erosion Cycle. 



The Jurassic and later erosion cycles have served to change 

 the areal geology from what it was during the Triassic to what 

 it is to-day. So far as the direct application to the Upper 

 Devonian problem is concerned, the chief effect has been to 

 remove such outlying areas as may have connected the present 

 outcrops in Pennsylvania and New York with those remaining 

 in the Green Pond axis. The northern limits must also have 

 been greatly restricted. 



There is, however, an indirect reason why these post-Triassic 

 cycles should be treated in some detail. We can perceive here 



