THE FRAMEWORK OF THE MOUNTAINS. Ill 



Mountains. If we carry our observations to the north flanks 

 of the Adiroudacks, there too, we find this sandstone. The 

 charming village of Potsdam is built on this sandstone a 

 classical spot which has given its name to a formation that 

 reappears in all countries. Here certainly, if nowhere else in 

 northern New York, the geologist receives a cordial greeting 

 and geology finds warm appreciators. This sandstone spreads 

 out horizontally to the St. Lawrence River. If we examine 

 the Adirondack slope on the west, the Potsdam sandstone is 

 found in its place, and even limestones come in succession, in 

 higher geological positions above the sandstone. On the 

 south we still find the sandstone. 



The appearance now is, that after the granite center had 

 burst through the gneisses, and all these rocks were standing 

 at a level somewhat lower than at present, the ocean still 

 covered the flanks now overlaid by the Potsdam sandstone, 

 and on the bottom of that ocean the sands were spread which 

 were destined to become consolidated as sandstone; then, after 

 this, there was a farther uplift of the -Adirondack mass, bring- 

 ing the Potsdam sands above sea-level, around their border, 

 and giving them also a tilt, while the gneisses received an in- 

 creased tilt. So the granitic center of the Adirondacks was at 

 first a small island ; then, by further upheavals, the island was 

 enlarged progressively on all its borders. 



Now let us proceed across the St. Lawrence valley. Here 

 we find horizontal Potsdam sandstone stretching up and down 

 the valley; and above this, a thick series of limestones. Con- 

 tinuing toward the Laurentide Hills, we see the horizontal 

 strata turning up gently. We ascend a gradual slope, "and 

 by and by, the limestones end. A steeper ascent is still under- 

 laid by the Potsdam sandstone. Here now, is the end of the 

 sandstone and we step on schists and gneisses and crystalline 

 limestones, each rising from under the preceding, until we 

 reach granitic rocks, which continue to the summit of the 

 ridge. Then passing still northward, we meet various for- 

 mations like those seen in ascending the ridge, but in the in- 

 verse order. In fact, the nature of the rocks, their altitudes 



