GEOLOGY OF THE NORTHERN ADIRONDACK REGION 285 



This submergence apparently completely overswept the old 

 Adirondack island, and that for the first time in its Paleozoic 

 history, with the possible exception of the latter part of the 

 Trenton. The whole of New York State would seem to have been 

 submerged and that for the last time in its geologic history. 



Later Paleozoic changes of level 



Toward the close of Utica time subsidence became again inter- 

 rupted and an upward movement was initiated. It was first 

 felt on the northeast, bringing the northern Adirondack region 

 again above the sea, and it has in the main remained a land area 

 from that time to the present. The movement of elevation pro- 

 gressed to the south and west till all of eastern New York had 

 been brought above sea level. From this time on the oscillations 

 of the southern and western borders of the present Adirondack 

 region now admitted the sea to unknown distances on the flanks 

 of the region, now again excluded it. Thus the Medina, Clinton 

 and Helderberg seas of the Siluric and Devonic quite cer- 

 tainly overlapped the margin of the region to some extent, and 

 later Devonic seas may well have done likewise. The district 

 was near the shore line of those seas, alternately received deposit 

 and experienced wear as the position of the shore line fluctuated. 

 The truncated edges of the deposits of those seas now come to 

 daylight to the south of the Mohawk valley in successive order 

 of deposit, their formerly existing extensions northward having 

 been worn away. Hence, while it is obvious that they formerly 

 extended considerably north of their present limits, the amount 

 of such extent is purely a conjectural matter. 



While the sea border was hugging the south and west sides 

 of the region, the remainder was out of water and so continued 

 with the possible exception of the submergence of a Champlain 

 valley strip during Helderberg time. Such a submergence is very 

 probable, but the amount of area so depressed is purely con- 

 jectural, the deposits of the time having utterly disappeared, 

 owing to subsequent erosion. This is, so far as known, the only 

 time that any portion of the northern Adirondack region has 



