GEOLOGY OF THE NORTHERN ADIRONDACK REGION 393 



siderable size, occupying approximately the same position as the 

 previous Beekmantown island, but with considerably diminished 

 acc;i, specially on the western side. As in that case, this land 

 was massed on the south and west. 



The only stratigraphic evidence of a break between the Black 

 Kiver and Trenton, seems to be in the upper Mohawk region, 

 where there is certainly a slight unconformity, with locally entire 

 removal of the Black River. In Trenton times also the Mohawk 

 region was but slightly submerged, and the formation is but 

 thinly developed. This would argue some shore line near at 

 hand, and Kemp's study of the Paleozoic outlier at Hope demon- 

 strates the presence of land near the southern Adirondack mar- 

 gin, during at least the early Trenton. 1 In addition, it seems to 

 the writer that this outlier presents suggestive evidence of the 

 truth of the arguments advanced in the preceding pages, regard- 

 ing the small extent of the invasion of the southern Adirondacks 

 by the successive seas. In this outlier Potsdam, Beekmantown, 

 Trenton and Utica strata are all present, and, with the possible 

 exception of the last, none of them seem to have been deposited 

 in great thickness, though during intervening periods of wear 

 some thickness of each may well have been removed. Apparently 

 the deposits indicate the near vicinity of a shore line to the north 

 in Potsdam, Beekmantown and early Trenton times, and their 

 thinness and character are due to such proximity. 



Throughout most of the Mohawk valley region the Trenton has 

 no great thickness, indicating but slight subsidence during its 

 deposition. On the east and west sides of the region, however, 

 it attains large thickness, hence subsidence was in progress on all 

 sides of the district, and the encroachment of the sea over it must 

 have considerably exceeded in extent even that of the previous 

 Black River sea. The Black River island must have been nearly, 

 if not utterly, wiped out by the close of the Trenton. 



Then came in the muds of the Utica, appearing first on the east 

 side of the region and gradually encroaching westward. Ruede- 

 mann's argument for the extension of the Utica over the entire 

 Adirondack region, based on the parallel alinement of the grapto- 

 lite fronds found fossil in the shales, as indicative of a uniform, 



^Sth An. Rep't State Geol. 189S. p.145-52. 



