GEOLOGY OF SARATOGA SPRINGS AND VICINITY 9 



recognizable over a large part of Canada and in the Upper Lake 

 region as well as in the x\dirondacks. 



A much later peneplain, of probable late Mesozoic date, was 

 also developed in the region, and again it was merely the local 

 development of a peneplain of wide extent in eastern North 

 America. Prior to its development, deformation of the region 

 had upwarped the older peneplain into the form of a gentle dome, 

 and at the same time downwarped the margins into shallow troughs 

 in which early Paleozoic sandstones, limestones and shales had 

 been deposited. The . ]\Iesozoic peneplain truncated the domed 

 summit of the older peneplain ; but on the margins of the region 

 the two surfaces intersect and the older passes beneath the younger. 

 The Paleozoic rocks lie upon the surface of the older, and the 

 younger cuts across them (figure i). An attempt to illustrate the 

 manner in which, by erosional stripping back of the Paleozoic 

 cover, portions of the old peneplain surface are exposed to view 

 at the margins of the Adirondacks, is seen in figure 2. 



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Fig. I Domed surface of Precambric peneplain, b b b, with marginal 

 Paleozoic deposits, both truncated by late Mesozoic peneplain, a a a. Verti- 

 cal scale much exaggerated. 



Fig. 2 Diagram in illustration of the manner of reaapearance of the old 

 Precambric peneplain at the present surface; a Z; = late Mesozoic peneplain; 

 c rf = tipped surface of old peneplain, in part covered by Paleozoic rocks; 

 from c to c, however, the Paleozoics have been recently removed by erosion, 

 reexposing the old peneplain surface; modern erosion has cut valleys in 

 both peneplain surfaces, but the ridge summits are remnants of these 

 surfaces. 



Since the development of the Mesozoic peneplain the highland 

 has been again uplifted, the uplift being greatest along the eastern 

 border. This has given the peneplain surfaces a tilt to the west. 

 Since this uplift the present valle\s of the region have been cut 

 below the surface of the Mesozoic })eneplain and, on belts of weak 

 rocks, have become ])roa(lly develoi)C(l. The entire surface of 

 the Saratoga and Schuylerville (juadrangles is below the level of 

 the ])cneplain, with the possible cxccj")tion of the hill sunmiits in 



