466 NEW YORK STATE MUSEUM 



This region of mature topography was then drowned by the 

 advancing Potsdam sea, the valleys first and later the highlands, 

 being covered by aqueous deposits. The Cambric strata are still 

 horizontal or nearly so, hence their position in the valleys must be 

 due to original deposition in depressions, and not to any kind of 

 folding. In some instances their position may be due to faulting, 

 but there was no evidence of such faulting in this region. 



Potsdam outliers are found in three localities within the Paradox 

 Lake quadrangle. One outlier is found on the extreme eastern edge 

 of the map in the valley of Trout brook; a second near Chilson, 

 outcrops in three localities, the intervening areas being drift- 

 covered ; the third two miles north of Sherman Corners. 



The Trout brook outlier lies in a valley of mature cross-section, 

 the present stream being rejuvenated and actively cutting. Were 

 the Potsdam removed the valley would show the gentle slopes 

 characteristic of a well established drainage line. The former 

 extent of the Potsdam is indicated by many loose boulders south 

 and west of the outlier. 



The Chilson outliers are masked in drift, but they indicate the 

 same thing — a mature Prepotsdam valley, drowned by the Potsdam 

 sea. . ' 



The Sherman Corners outlier is now being cut by a vigorous post- 

 glacial stream'. The outline of the hills suggests that in this case 

 also if Potsdam and glacial deposits were removed the valley would 

 be mature. 



The conclusion then seems inevitable that the main drainage lines 

 were established in Prepotsdam time. The Trout brook valley, 

 the Putnam^ creek valley and the valley two miles north of Sherman 

 Corners are shown to be of Prepotsdam age by the outliers. By 

 their similarity in stage of development the valleys of Chilson lake 

 and of Paradox lake would appear to belong to the same period. 



The Schroon valley is problematic in age and in origin. The 

 largest valley on the quadrangle, it passes through the anorthosites 

 with glacial terraces masking its sides. No limestone has been 

 found in its basin, nor any Potsdam sandstone. The topography 



