234 J. Barrett, — Upper Devonian Delta of the 



be postulated. Thinning at the rate of thirty feet per mile 

 would cany the margin of the Upper Devonian to the north- 

 ern shore of Lake Ontario over Ordovician rocks, and over the 

 southern part of the pre-Cambrian now exposed in the Adiron- 

 dacks. A rate of 20 feet per mile would carry the margin 

 some thirty miles farther north. The regional dip of the base 

 of the Lower Devonian would project such a marginal exten- 

 sion upward high over the pre-Cambrian as now exposed. The 

 present elevated position of the pre-Cambrian in that region 

 cannot date back to the Devonian, so that this degree of exten- 

 sion of the Devonian strata meets with no structural difficulty. 



Evidence from the Green Pond Mountain Region. 



The discussions on the original limits of the Upper Devo- 

 nian, based on the evidence of the margins, have been of the 

 nature of an extrapolation, determining the rate of changes 

 at the margin and projecting them to their limits. To give 

 confidence to such conclusions they must be supported by inde- 

 pendent lines of evidence. One of the strongest of these is 

 found in the sediments of the Green Pond Mountain outlier, 

 downfolded and downfaulted into the pre-Cambrian rocks 

 twenty-five miles southeast of the marginal outcrop of the 

 Catskill formation. The present isolation of the syncline and 

 the different character of many of the formations within it 

 have led a number of geologists to the opinion that this was a 

 separate basin of deposition. In regard to this view, however, 

 Kiimmel and Weller state : 



" Darton and Walcott have held that the rocks of this region, 

 at least those subsequent to the Cambrian limestone, were depos- 

 ited in an inlet separated by a land area on the west from the 

 great sea, which lay still further west. We have observed no facts 

 in the New Jersey area which necessitate this assumption. On 

 the contrary, we believe that the weight of evidence there favors 

 the view that these formations were formerly continuous with the 

 corresponding beds in the Kittatinny valley and northwestward. 

 Recognizing, however, that the evidence in New Jersey is not 

 decisive, and not having had an opportunity of examining criti- 

 cally the field in New York, we are unwilling to oppose the con- 

 clusions of these workers, although from what we have seen we 

 are inclined to believe that the facts are capable of a different 

 interpretation from that of Mr. Darton. In any event, there can 

 be no doubt but that the seas in which these beds were formed 

 had a much wider extension than the present area of the for- 

 mation." * 



A discussion of the stratigraphy as given below suggests that 

 the conclusion of Kiimmel and Weller may be more positively 



* The Books of the Green Pond Mountain Eegion, Ann. Eeport New Jersey 

 Geol. Surv. for the year 1901-1902, p. 40. 



