1883. 23 Trans. N. V. Ac. Scu 



the eastern flank of the range. Between Bloomingburg and Wurts- 

 boro the mountain has been pierced by a railway tunnel, 3,857 feet 

 long, and 340 feet below the summit of the mountain, which passed 

 first through the Hudson River shales, and then through 850 feet of 

 the Shawangunk grit, the beds standing at an inclination of about 60° 

 toward the northwest. 



Two systems of joints occur in this stratum — the one along the strike, 

 N. 20° E. and S. 20° W., the other transverse, N. 60° W. and S. 60° E. 

 With the latter are connected the lodes of galena and sphalerite at 

 Ellenville, Homowack, and Wurtsboro, associated with crystallized 

 quartz, pyrite, and chalcopyrite. 



The general construction of the mountain, with its flat cap of 

 conglomerate, its escarpments, and its view of the Great Valley and 

 Hudson River, is suggestive of that of Lookout Mountain, Tenn.; 

 and there is a further analogy in the abundance of huge rectangular 

 masses of the rock, which have separated more or less from the edge 

 of the escarpments, along the lines of the joints, but whose movement 

 has sometimes been so small as to be distinguishable only at a dis- 

 tance by the slight alteration of the angle of dip. Such movements, 

 often attributed to the action of floods, earthquakes, or ice, have been 

 plainly caused here, as in the enormous conglomerate blocks of the 

 "Ruined City," at Lookout Mountain, Tenn., and the similar fantastic 

 masses along the precipices of the Catskills, by the slow undermining 

 effect of rain-water and frost upon the underlying strata of thinly 

 laminated grits and Hudson River shales. Some of the great and 

 deep clefts, which result from these movements, form the natural " ice 

 caves " of Napanoch and other points along the range. 



Mather long ago has shown that " the Mamakating and Wallkill 

 valleys, forming the Great Valley, an extension of the Champlain 

 and Hudson valley, from its southwestwardly trend, would be in the 

 natural direction of the set " of the ice current down that valley. The 

 Shawangunk range, stretching along the western boundary of the 

 Great" Valley, received the full force of the ice-pressure and movement, 

 of which a faithful and exact record remains to us in the character of 

 its glacial erosion. 



We will consider first the records of glaciation in the surrounding 

 region. On the east side of the range, the rocks of the Wallkill val- 

 ley consist chiefly of the Hudson River shales and lower soft shales 

 and limestones, which have retained glacial markings only in excep- 

 tional localities, and most of which are buried beneath a thick layer 

 of drift gravels, sands, and clays of Champlain age. 



Both pebbles and huge boulders of many varieties of foreign rocks 

 are scattered through and over this layer. Thus, near Newburg, I 



