496 Russell — Relations of the Great 



there is no evidence of such a tremendons horizontal 

 displacement. The second theory would be reasonable, 

 if it conld be shown that the dip of the plane of the Great 

 Fanlt were as small, or the throw of the cross faults as 

 great, as is demanded. The throw of the Paug-Bluff 

 Head fault is about 2,500 feet where it intersects the 

 Great Fault, and possibly 3,000 feet further northeast, 

 and the Great Fault seems to be offset between a mile and 

 a half and two miles. A dip of the fault plane of 14° to 

 21° would be required to produce this offset. This 

 difficulty is more serious even farther north, where the 

 offset seems to be several miles. The throws of these 

 faults are given by Davis as about half a mile, and even if 

 it be assumed that they increase to the northeast, an 

 extraordinarily low dip of the fault plane must be 

 assumed to account for the offset. 



The question might be settled by finding fanglomerates 

 and the pre-Triassic quartz lode along the cross-faults 

 where they bound the Trias sic. Near Durham, where the 

 portion of the fault examined ended, there was an outcrop 

 of the fanglomerate and the quartz lode which were 

 apparently associated with the cross fault. This inter- 

 esting problem cannot be settled without further investi- 

 gation, but the evidence seems to favor the third hypoth- 

 esis. 



The Physiography of Newark Time. 



During the deposition of the Newark sediments of the 

 region periods of movement along the fault plane alter- 

 nated with times of relative repose. This is shown by the 

 fact that at some horizons fanglomerates occur near the 

 fault plane, while at others fine shales and sandstones are 

 found. The average rate at which the fault scarp rose 

 above the plains to the west during Newark time was 

 probably not rapid, perhaps something like one foot in a 

 thousand years. It is probable, therefore, that the scarp 

 was at times reduced to a gentle slope. If the same hori- 

 zon is followed till it intersects the fault plane in several 

 places, it is sometimes found that fanglomerates are 

 developed in the horizon at some of these places and not 

 in others. The rivers may have caused this by building 

 alluvial fans only where they issued on to the plains, or 

 it may be due to unequal movement of different portions 

 of the fault. 



