44 ^'EW YORK STATE MUSEUM 



seem to indicate that the southern Adirondack region could not have 

 been completely submerged at the close of the Lower Silurian, much 

 less so at the close of the Trenton." 



PLEISTOCENE (GLACIAL) GEOLOGY 



From the standpoint of its glacial history the Port Leyden district 

 is tmusually interesting and instructive. When the great ice sheet, 

 which covered most of New York State, reached its maximum 

 development the Black river valley must have been buried under 

 several thousand feet of ice. We know this because the whole 

 Adirondack region is glaciated and was covered by the ice. The 

 advance and retreat of the ice across the Port Leyden quadrangle 

 has left most of the ordinary marks of glaciation, while certain of 

 them are developed to a remarkable degree. So far as the writer 

 knows nothing has been published regarding the Pleistocene history 

 of this immediate region, although a report by Chamberlin^ pub- 

 lished some 2y years ago has an indirect bearing.^ 



Direction of ice flow^ 



Chamberlin, in the report above referred to, makes the tentative 

 statement '' that massive ice currents having their ulterior channels 

 in the Champlain valley, on the one hand, and the St Lawrence on 

 the other, swept around the Adirondacks and entered the Mohawk 

 valley at either extremity, while a feebler current, at the hight 

 of glaciation, probably passed over the Adirondacks and gave to the 

 whole a southerly trend." Observations by later investigators have 

 tended to bear out this view and the evidences from the Port Leyden 

 quadrangle herewith presented have an important bearing upon the 

 proposition. 



The direction of flow is best shown by the glacial striae which 

 have been observed at a number of different places through the 

 district. The striae are best preserved upon the hard Precambric 

 rocks, but these are mostly drift covered "except along the chief 

 stream courses. The limestones are next most favorable while upon 

 the shales none have been found. Striae are present only upon those 

 surfaces from which the drift has been recently removed, because 



'U. S. Geol. Sur. 3d An. Rep't 1881-82. p. 36(^65. 



^ Since the above was written Prof. H. L. Fairchild has presented several 

 papers, bearing on the glacial history of northern and central New York, 

 before the 1908 meeting of the Geological Society of America. These papers 

 will be published in the bulletin of the society 



