Appalachian Geosyncline. 99 



erosion to note the fatal weakness in the structures of the 

 Appalachian geosyncline. The three notably resistant forma- 

 tions, the Kittatinny, Pocono, and Pottsville formations, are 

 separated and underlain by great thicknesses of non-resistant 

 rocks. Wherever this series is exposed to erosion the rivers 

 rapidly sink toward baselevel upon the soft formations and the 

 mountain-makers become separated by deep valleys. Each is 

 sapped from all sides. It is the old proverb — united we stand, 

 divided we fall — applied to geology. It is not thought, from 

 other considerations, that the Upper Devonian ever extended 

 over the Connecticut Valley. It is concluded, however, in the 

 following parts of this article, that, as shown in fig. 1, it once 

 thinned out over the region now occupied by the Triassic in 

 lew Jersey and Pennsylvania, but was destroyed before the 

 beginning of the JSTewark deposition. The conclusion is made 

 more impressive by noting that on the Susquehanna River the Tri- 

 assic rests on Cambro-Ordovician limestone. Only eight miles 

 north lies the ridge of Silurian quartzite. Beginning with this 

 formation, four miles of strata, including Devonian, Mississip- 

 pian, and Pennsylvanian formations, rise vertically in the 

 somewhat overturned arch of the syncline. The great eleva- 

 tions which they imply on the east, even though they rapidly 

 thinned out in that direction, had been removed before the 

 beginning of Newark time. 



The Newark Erosion Cycle and the Quartzite Conglomerates. 



The Newark group of red shales and sandstones occur in a 

 number of isolated areas from Nova Scotia to North Carolina. 

 The one which enters into 'the present discussion is the New 

 York- Virginia area. This shows a monoclinal structure, dip- 

 ping northwest at average inclinations of 15 to 20 degrees, but 

 broken by faults. As interpreted by the present writer, the 

 structure across the basin during sedimentation appears to have 

 been analogous to that which exists at the present time across 

 the Great Valley and Sierra Nevada of California. There, 

 uplift on the east, downsinking on the west during the later 

 Tertiary has given rise to profound erosion of the uplifted side 

 and transfer of sediment on to the sinking floor. A fault zone 

 separates the Great Valley, the downsunken side of the block, 

 from the Coast Ranges. The latter contribute sediment to the 

 valley, but the greater part comes from the crystalline rocks of 

 the Sierras. 



The northwestern boundary of the Triassic rocks is shown 

 on the map, fig. 1. On the north it lies ten miles southeast of 

 the Upper Devonian Skunnemunk conglomerate and thirty- 

 three miles from the present Catskill margin. From there it 

 trends south west ward across the structure, gradually approach- 



