58 NEW YORK STATE MUSEUM 



of Precambric rock materials must have been removed because the 

 Precambric rock structures (fohation, folding etc.) immediately 

 below^ the Potsdam could have been formed only at great depths. 

 We also knov^ that this work of erosion progressed far enough to 

 reduce the whole Adirondack region to the condition of a more or 

 less perfect peneplain. The character of this old peneplain surface, 

 upon which the Paleozoic rocks rest, has been carefully studied on 

 all sides of the Adirondacks, and it is known to be moderately 

 rough in the northeast and very smooth in the southwest. Within 

 the Lake Pleasant quadrangle the old peneplain surface has of 

 course been modified beyond recognition by subsequent elevation, 

 faulting, and erosion, but from what we know about it within the 

 Little Falls, Broadalbin, and Saratoga quadrangles, we can be sure 

 that, during the late Cambric period, there could not have been 

 more than an occasional knob perhaps 50 or 75 feet high projecting 

 above the general surface. 



This peneplain gradually became submerged under the sea when 

 the Potsdam, Theresa, and Little Falls seas successively encroached 

 upon the Adirondack region. As shown by the marine character 

 and present distribution of the Potsdam, Theresa, and Little Falls 

 deposits, these waters must have spread over the whole southeastern 

 Adirondack region including all the Lake Pleasant quadrangle 

 except possibly the northwestern portion. In the paper above cited 

 reasons are given for thinking that this late Cambric shore line 

 passed through, or close to, the northwestern portion of this quad- 

 rangle. 



Toward the close of the Cambric period, a general emergence 

 of the whole southern Adirondack area brought our region above 

 sea level as proved by the distinct unconformity at the summit of 

 the Little Falls dolomite. 



During Beekmantown and Chazy times we have no positive evi- 

 dence regarding the physiographic condition of our region because 

 rocks of those ages are wholly lacking. If such rocks were de- 

 posited, and this is unlikely, they were removed by erosion before 

 succeeding Black River time. 



During Black River (Lowville) time the area of the quadrangle 

 must have been almost, if not quite, all under sea water because of 

 the presence of such rocks in the outliers at Wells and near Hope. 

 The distinct unconformity at the summit of the Black River 

 (Lowville) limestone shows that our region again emerged from 

 the sea and underwent erosion. 



