GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 7 



New Haven and Hartford. Ferries cross between Fishkill Land- 

 ing and Newburgli and between Poughkeepsie and Highland on the 

 West Shore Railroad. 



TOPOGRAPHY 



East of the Hudson the topography is chiefly that of a rolling 

 upland of moderate elevation, which is due in part to the nature 

 and structure of the underlying rock formations as affected by 

 erosion, and in part to the mantle of glacial deposits. 



Along the southern margin of the quadrangle are several rugged 

 spurs of the Highlands. These are bold, often precipitous, and 

 usually wooded. They are known as the Fishkill mountains, receiv- 

 ing their name from old Fishkill township, of which they are a part. 

 These mountains are made up chiefly of Precambric gneisses and 

 are flanked by and faulted with the Paleozoics of the valley. 



The westernmost Highland spur is the northern extension of 

 Breakneck mountain ridge and the part within this quadrangle is 

 known as Bald hill (see plate i). It has a maximum elevation of 

 1540 feet. The Mount Honness spur next east has an elevation 

 of 840 feet at its northern extremity. Mount Honness proper, but 

 reaches a height of 1300 feet near the quadrangle boundary (see 

 plate 2). A short spur east of Honness, with an elevation of 

 885 feet, separates it from Shenandoah mountain, which has a 

 maximum height of 11 15 feet. East of Shenandoah mountain the 

 Highland mass attains an elevation of 1232 feet at " Looking Rock," 

 which is at the summit of the steep northwestern slope. This 

 spot is widely known because of its fine view. 



North of the Fishkill mountains the rocks within the quadrangle 

 are principally shales, slates, grits, phyllites and limestones. The 

 more metamorphic character of these strata as they are followed 

 eastward from the Hudson finds expression in the higher elevation 

 of the slate and graywacke in the northeastern part of the area. 

 Here the hills in places reach a height between 700 and 800 feet. 

 West of the Hudson the average elevation in the slates and grits is 

 greater than on the east of the river, often attaining 400 to 600 

 feet. " Illinois mountain," the northern extremity of Marlbor- 

 ough mountain, is 1105 feet high. 



In contrast to the heights is the gorge of the Hudson, which 

 borings have shown reaches a depth near Storm King of over 

 700 feet. 



