52 NEW YORK STATE MUSEUM 



thickness of the Potsdam sandstone as shown in the nearby areas, 

 it seems clear that this Grenville mass must have risen fully seventy- 

 five feet above the surrounding country (peneplain) just before 

 Potsdam submergence. About two-thirds of a mile south-southwest 

 of North Galway the passage beds are practically in contact with 

 the Precambric so that we have here another, but smaller, hillock. 

 The relations are not so well shown around the Grenville area on 

 the west side of the Amsterdam reservoir but doubtless this, too, 

 represents a low knob which rose above the general level of the 

 peneplain. The locations of these knobs or hillocks have no doubt 

 been largely determined by the very hard and resistant character 

 of the quartzite which, of all the Grenville rocks, would stand out 

 longest against atmospheric action prior to, and wave action during, 

 Potsdam submergence. 



North of Barkersville the mapping suggests an uneven surface 

 but positive evidence was not found. In the small Potsdam area 

 just east of Northville the beds are practically horizontal and they 

 appear to occupy a depression in the Precambric but, because of 

 nearness to the fault, the amount of unevenness can not be satis- 

 factorily determined. Elsewhere within the quadrangle the char- 

 acter of the Precambric surface can not be studied. 



During the early Paleozoic there were certain minor oscillations 

 of level (already referred to) when at times the region was a low 

 lying land area undergoing erosion. For most part, however, the 

 whole district was under water and remained so until after the 

 deposition of all the Paleozoic sediments when a great uplift, with- 

 out folding but with some tilting of the strata, brought the whole 

 Adirondack region (then mantled with sediments) well above the 

 water. This uplift probably occurred at the close of the Paleozoic 

 era. The simple elevation of this ocean bottom would have given 

 rise to a comparatively smooth and featureless topography, but it 

 is generally considered that the faulting of the eastern Adirondacks 

 accompanied the uplift. As Gushing says :^ " The forces which 

 folded the region to the eastward affected the Adirondack district 

 but slightly and the rocks are not folded. But in the reaction of 

 the region from compression, tension faulting took place on a large 

 scale, and its eastern portion was sliced by a series of meridional 

 faults which cross it." According to this the topography of the 

 Broadalbin district was that of the uplifted sediments which were 

 greatly dissected and increased in ruggedness by the faulting. 



1 N. Y. State Mus. Bui. 95, p. 421-22. 



