Branner.] OOO [Feb. 10, 



original, I find that the influence of topography upon the movement of 

 the ice was given, as an explanation of double striation, by Mr. C. E. 

 Hall in the Proceedings of the American Philosophical Society, Novem- 

 ber 5, 1875 (pp. 633-4). The expression in this place of his theory 

 upon the subject, is the most explicit I have seen. Prof. N. H. 

 Winchell published an article in the Popular Science Monthly in 1873 upon 

 "The Drift Deposits of the Northwest," in which he refers to the 

 influence of valleys upon the edge of the ice. Mr. T. C. Chamberlin, in 

 his "Terminal Moraine of the Second Glacial Epoch," refers in many 

 places to the influence of topography on the direction of glaciers, and no 

 doubt there are many other references to, and observations upon this sub- 

 ject which I have not been able to consult. 



If, in recording the facts observed, I have been led to what may possi- 

 bly be regarded as theorizing, my only defence is that it was quite impos- 

 sible to see all about me the evidences of so wonderful, so awe-inspiring 

 phenomena without coming to some conclusions regarding them. Then, 

 too, in his letter transmitting Report Z of the Second Geological Survey 

 of Pennsylvania, Professor Lesley has thrown no little doubt over the 

 physical questions connected with glaciation, and, whether his suggestions 

 there be open questions or not, they are calculated to make young geolo- 

 gists observe the evidences of glacial phenomena with a view to arriving 

 at rational conclusions in regard to these questions. 



The accompanying maps are necessarily upon a scale too small to con- 

 vey a proper idea of the influence of the topography upon the movement 

 of the ice. To show this a map would need to be very detailed and exact, 

 and upon an unusually large scale, or better still, a large model would be 

 required. 



I take great pleasure in acknowledging here the kind encouragement of 

 Professor Lesley and of Mr. Ashburner. To Mr. Geo. M. Lehman I am 

 indebted for a number of valuable observations upon the direction of 

 stria; in various places, and to Sheldon Reynolds, Esq., of Wilkes-Barre, 

 for some observations made in the vicinity of that city. 



Physical Features. 



The Wyoming and Lackawanna valleys are, properly speaking, a 

 single closed and curved synclinal valley, about fifty miles long by about 

 five miles wide at its widest part, and bounded by mountains which 

 coalesce at the extremities of the valley. 



The concave side of its crescent form faces toward the north-west, the 

 north-east end of the basin bearing about N. 20° E., and the south-west 

 end bearing S. 70° W. Its mountain barriers thus presented themselves 

 to the ice sheet at various angles, and now offer a valuable opportunity 

 for observing the influence of such barriers upon the ice flow. Within 

 this great basin are many secondary or miniature basins with a general 

 resemblance to the large one, and many low, gently undulating and regu- 

 larly sloping hills, some of which are anticlinals, and some are ridges 



