GEOGRAPHIC DISTRIBUTION. 241 
level of the Potsdam sandstone which surrounds it. Its summit attains 
an altitude of 1,500 feet, with the Potsdam reaching up to 1,300 feet on 
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Figure 1.—Sketch Map of Clinton County, New York. 
Showing by heavy black line the Potsdam-pre-Cambrian boundary and location by numbers of the 
syenite-porphyry dikes. 
its western flank. The area of pre-Cambrian rocks exposed is about 8 
square miles, within which are found 8 out of the total number of 14 of 
these dikes now known. Here would seem to have been a center of the 
