J2 NEW YORK STATE MUSEUM 



schist, the ore often preserves the appearance of banding and cleav- 

 age, and not uncommonly carries a small percentage of graphite, 

 the only mineral that seems to have successfully resisted the solvent 

 action of the iron-bearing solutions. 



As to the source from which the iron has come, the explanation 

 advanced by C. H. Smyth jr, merits full acceptance since it meets 

 the conditions surrounding the geology of the deposits. His theory 

 is that the iron has been derived from pyrite and magnetite, which 

 occur abundantly in the schist in the immediate vicinity of the ore 

 bodies. By oxidation the pyrite would yield ferrous and ferric 

 sulfates, which would be readily taken up by the underground 

 circulations. Free sulfuric acid would also result and react upon 

 the veins and disseminations of megnetite. By reaction with the 

 limestone and the minerals of the schist, the solutions would de- 

 compose and the iron precipitate as carbonate and limonite. By 

 subsequent alteration these minerals have been changed to hematite. 

 Residual masses of carbonate are occasionally found in the deposits. 

 Whenever the Potsdam sandstone is found in contact with the ore, 

 the lower layers show a deep iron stain, evidently the effect of 

 impregnation by the iron-bearing solutions. 



The fourth class of iron ores, the limonites, are not of much im- 

 portance in the Adirondack region. The deposits are, as already 

 stated, superficial accumulations due to the washing and leaching of 

 the neighboring rocks and soils. They seldom, if ever, exist of 

 sufficient size and richness to repay working, at least under present 

 conditions. 



On Tuesday an excursion to Keeseville and the Ausable chasm 

 was made by train and tallyho. Professors Woodworth and Gush- 

 ing showed the party the marine delta of the Ausable river, the 

 former lake shore lines, the post-Hochelagan gorge of the Ausable 

 river cut in Potsdam sandstone, the Potsdam conglomerate, the 

 northern slope of Trembleau mountain, and the anorthosite. 



In the evening at the Champlain Club Prof. H. P. Gushing dis- 

 cussed tlie 



Evidences of physical oscillations during the Cambro-Silurian 



in northeastern New York 



as brought out by a general study of the stratigraphy of the region. 

 There was a great Potsdam subsidence on the northeast, diminishing 

 to zero westward. The succeeding Beekmantown depression en- 

 croached further on the land than did the Potsdam on the southern 



