8 NEW YORK STATE MUSEUM 



leaves the map, to the summit of Hamilton mountain, whose alti- 

 tude is 3250 feet. The Hamilton-Swart mountain mass is the 

 largest and highest of the whole area. It is 5 miles long, 2 miles 

 wide, and has several peaks whose elevations range from 2000 to 

 3250 feet. Next in order comes the Three Ponds-Blue Ridge 

 mountain mass some 4 or 5 miles long, 2 or 3 miles wide, and with 

 several peaks ranging in altitude from 2800 to 3000 feet. Specu- 

 lator mountain, with an altitude of 2973, stands out prominently in 

 the northern part of the quadrangle. In the southwest, the Moose- 

 North Branch mountain mass shows altitudes from 2500 to 2800 

 feet. In the southeast, the Cathead mountain ridge rises to 2427 

 feet. Just west of Wells, the Mount Rouge-Dunham ridge stands 

 out very prominently as viewed from the east across the valley 

 (see plate 9). This ridge has a number of peaks reaching alti- 

 tudes from 21 17 to 2646 feet. These and many other prominent 

 ridges trend from north-south to northeast-southwest due to 

 faulting. 



From the geological standpoint the features of principal interest 

 are : the variety of Precambric rocks ; the two important Paleozoic 

 rock outliers ; the dissection of the region by numerous faults ; and 

 the glacial phenomena. 



The oldest rocks are members of the Grenville series which are 

 classed with the most ancient known rocks in the crust of the earth. 

 They are chiefly highly metamorphosed stratified rocks, and are 

 much less abundantly developed here than is usual in the Adiron- 

 dacks. 



A small area of anorthosite-gabbro in the northeastern corner 

 of the quadrangle is probably of the same age as with the great 

 body of anorthosite in Essex county. 



Next in age come various phases of the syenite-granite series. 

 These include augite and hornblende syenite to diorite, granitic 

 syenite, granite, and granite porphyry. These have all been intruded 

 into the Grenville and hence are younger though also metamor- 

 phosed. They are by far the most abundant rocks of the quadrangle. 



Gabbro of the usual Adirondack sort occurs at several places. 

 Diabase, in the form of a few small dikes, is the youngest of the 

 Precambric rocks. Both gabbro and diabase are here less common 

 than in the eastern Adirondack region. 



The Paleozoic rocks are wholly confined to the outliers in the 

 valleys at Wells and near Hope. Cambro-Ordovicic strata, includ- 

 ing Potsdam sandstone, Theresa sandstone and dolomite. Little 



