Lower Helderberg Rocks of Port Jervis, etc. 291 



Rock, at the southern extremity of which it receives the 

 waters of the Neversink River. Tri-States Rock has a local 

 reputation, because in the year 1874, I think, members of 

 the U. S. Coast Survey were for a time stationed upon it, 

 to determine its exact latitude and longitude. The bound- 

 ary lines of three states, New York, Pennsylvania, and New 

 Jersey, unite in a point upon this rock. It is about one-half 

 mile outside the corporate limits of Port Jervis. 



The geological boundaries are very sharply defined. The 

 Shawangunk Mountain, called Blue Mountain in New Jersey, 

 and Kittatinny Mountain in Pennsylvania, extends from the 

 vicinity of the Hudson River, in Ulster County, nearly to 

 the Maryland line, a distance of 240 miles ; and its south- 

 eastern front, when not buried under the piles of drift 

 material which seem to have been poured through the low 

 notches in its crest line, or softened by the uplifted shales of 

 the Cincinnati Group, marks very plainly the beginning of 

 the rocks of the Upper Silurian age. The westward-bound 

 traveller upon the Erie Railway, may easily see the un- 

 conformable junction of the Shawangunk Grit, or Oneida 

 Conglomerate, with the older shales of the Cincinnati Group, 

 if he will look out of the right-hand window as he enters 

 the rock-cutting a little west of Otisville. After running 

 for some distance along the western slope of the Shawan- 

 gunk, the reddish, banded, ripple-marked and sun-cracked 

 surfaces of the Medina Sandstone formation, come into view. 

 These continue until the road turns shortly to the right, and 

 crosses a narrow, eroded valley, made at the expense of some 

 of the strata of the Lower Helderberg Group, which, in a 

 smoothed and striated condition, were uncovered to procure 

 the earth (drift) to make the embankment. The train then 

 plunges into another rock-cutting, made through a declining 

 "tail" of Cauda Galli Grit. Along the north-west slope of 

 this latter ridge for a mile or two, may be seen many exam- 

 ples of "crag and tail" structure, of glacially smoothed and 

 striated surfaces, and, just as the road curves sharply again 



