﻿Pennsylvania during the Glacial Epoch. 365 



seen. They bear S. 84° W., magnetic. The point at which 

 these strise were observed is about fifty feet southeast of the 

 triangulation station on the summit of the north knob of Elk 

 Mountain. The elevation of this knob, according to Professor 

 I. C. White, is 2,700 feet above tide.* 



It has been supposed hitherto that we could measure the 

 thickness of the ice in this part of the country upon the sides 

 of these high peaks. The finding of well-defined strias upon 

 the very summit of the highest of them leaves us without a 

 measure for the thickness of the ice in northeastern Pennsyl- 

 vania. Other high points, such as Ararat, 2,600 feet, and 

 Sugar Loaf, 2,450 feet above tide (White), only seven miles 

 away and lower than Elk Mountain, must, almost necessarily, 

 have been buried beneath the ice, although Professor White 

 found no evidences of ice action upon their summits. The 

 whole range of the Lackawanna Mountains northeast of the 

 Susquehanna gap at Pittston has been examined by the writer. 

 Evidences of glaciation were found upon its highest points 

 along its entire length, or as far at least as Stillwater, above 

 Forest City, where the Lackawanna Eiver cuts through the 

 range. The top of Bald Mountain, perhaps the highest point 

 in this part of the range, and about 2,200 feet above tide, is 

 striated in many places, while many bowlders, which seem to 

 have been pushed up the northwest face of the mountain from 

 the ledge not far below, are scattered over its summit. The 

 strise upon this eminence bear S., S. 6°, 10°, 11°, 20°, 25°, 33° W. 



All my observations along the summit of the Lackawanna 

 Mountains, and upon the high points here referred to, go to 

 show that the great body of ice- and water-worn material ends 

 long before the highest elevations are reached. In ascending 

 Elk Mountain I did not see a single water-worn fragment above 

 about 2,100 or 2,200 feet, though it would be extremely rash, 

 of course, to say that such fragments do not exist above this 

 elevation. This observation agrees entirely with those of Pro- 

 fessor White. 



It cannot be said that the disappearance of what was sup- 

 posed to be the measure for the thickness of the ice in north- 

 eastern Pennsylvania, upon the sides of Elk Mountain, was 

 altogether unexpected. The study of the topography and gla- 

 ciation of the Lackawanna and Wyoming Valleys had already 



* Report G5, Second Geol. Survey of Pa., p. 136. I have used the elevations 

 given by Professor White for these summits, because he checked and re-checked 

 them from Herrick Center, four miles away. When not otherwise specified, the 

 measurements mentioned in this paper have been furnished me by Mr. D. N. 

 Green, of Scranton, who used the railway elevations at Carbondale or Scranton as 

 a base. I believe his elevations have not been checked. He does not make the 

 elevation of the north knob of Elk Mountain as great as Professor White by 

 sixty feet. 



Am. Jouk. Sci. — Third Series, Vol. XXXII, No. 191. — November, 1886. 

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