THE ADIRONDACK MOUNTAINS 55 



Of course the topographic oiitHnes have been notably modified by 

 weathering and erosion. This valley at Wells has been referred to 

 somewhat in detail because it so clearly illustrates the principles of 

 Adirondack faulting. 



\\ hen were the faults developed? That at least some fracturing 

 occurred in Prepaleozoic time has been established, but, so far as 

 known, such faults have relatively little influence upon the existing 

 relief features. Also it is probable that fault movements took place 

 during the Paleozoic era, but if so the old fault cliffs or ridges must 

 have been practically obliterated by erosion during the Mesozoic 

 era concluding with the development of the great plain of erosion 

 already described. If so, how do we account for the present Adiron- 

 dack ridges and valleys which owe their existence chiefly to fault- 

 ing? Accompanying the uplift of the peneplain there was either 

 much faulting for the first time, or renewed faulting along old lines 

 of fracture, or, as a result of unequal erosion due to differences in 

 rock character on opposite sides of old faults, new cliffs or scraps 

 began to be produced. That much of the faulting actually dates 

 from the uplift of the peneplain, or possibly even later, is proved 

 by the existence of certain steep cliffs in perfectly homogeneous 

 rock masses and by the distinct tilt of many of the fault blocks, both 

 of which features have been scarcely modified by erosion since 

 their development. 



Cenozoic History not Including the Ice Age 



Development of existing major relief features. The uplift of 

 the great peneplain was an event of prime importance for northern 

 New York because it literally furnishes us with the beginning of the 

 history of most of the principal existing relief features of the region. 

 Hence we reassert with emphasis that the chief topographic features 

 of the State have come into existence since the uplift of the pene- 

 plain because they have been produced by the dissection of that 

 upraised surface. This dissection was largely the work of erosion, 

 though, as already explained, faulting .produced notable topographic 

 effects in the eastern and southeastern Adirondacks. Also it should 

 be borne in mind that the central to east-central Adirondack area 

 stood out with many masses above the general peneplain level. 

 Since the uplift, however, this area has been deeply trenched and 

 made very rugged as we see it today. All the great valleys around 

 the Adirondacks — the St Lawrence, Champlain, Mohawk and 

 Black river — have been carved out of the upraised peneplain, 



