1895.] 387 [Lyman. 



north of the western end of the railroad station (and the station is 

 so close beyond the bridge that a small corner of the platform can 

 be seen in the picture, beyond the right-hand abutment) an artificial 

 rock exposure begins and extends nearly fifty yards westward, with un- 

 mistakable dips of forty degrees, south about fifty-three degrees ■west. 



7. In the space, however, between tlie danger-post and the strongly 

 marked dips of the eastern half of the eastern view, the structure is not 

 so uniform, and is not so clearly shown by the photograph, nor indeed so 

 easily made out on the ground. Ten j'ards along the cutting east of the 

 danger-post and opposite the eastern end of a small stable on the top of 

 the south side of the cut, and in the picture a little to the left or directly 

 beneath the right-hand telegraph pole, in the rather smoothly rounded 

 projecting rock mass, there is a small rock saddle, or anticlinal, that can 

 be seen on the ground with some care, and can even be perceived in the 

 photograph, especially where the layers about the midheight of the cut 

 begin to bend over from the westerly dip. Six yards further east, on the 

 western side of the first small depression or slight gully, and five yards 

 west of the first strongly marked southwesterly dip surface, and in the 

 picture almost directly below the telegraph pole, there is a small rock 

 basin or synclinal, somewhat diflicullly discerned in the photograph, yet 

 still decidedly perceptible there with a little patience, particularly with 

 the help of a strong magnifying glass, and quite visible on the ground. 

 The partly obscure portion of the section, then, is at most a dozen or fif- 

 teen yards of the length of the cutting ; and at right angles with the 

 strike not more than eight or ten yards ; and, as the photograph shows, 

 it is apparently not the part represented by Prof. Lewis's sketch. It 

 appears unfortunately impossible to make the dips of that portion ex- 

 tremely obvious in a photograph ; but on the ground they can be seen 

 with a little care, and have been distinctly recognized, not only by my- 

 self, but by Mr. Harden, and, in December, 1888. by Dr. Amos P. 

 Brown and Mr. J. S. Elverson. The place is now so precisely pointed 

 out that it can readily be identified by any one visiting the spot, and he 

 can see for himself the accuracy of the description of the structure. 



8. It is evident, then, that the rocks of the cutting are by no means 

 fault rock, but merely steep-dipping and somewhat folded dark gray 

 and dark red beds of the Gwynedd Shales, cut across at a sharp angle 

 with the strike and much fractured with ordinary cleavage planes of 

 many directions, and requiring for a perception of the structure to be 

 observed at an angle of not more than forty-five degrees with the railroad 

 instead of at right angles. The chief geological interest and value of the 

 rock exposure, therefore, is not in its displaying a fault of otherwise 

 incredible dimensions, with the unheard-of width of a hundred feet or 

 more, and with the inconceivable heave of four or five miles for a nearly 

 vertical trap dike ; but in its showing how it may sometimes be a little 

 difficult to distinguish the true bedding and dip among many confusing 

 cleavage planes. The great fault, coming westward from the southern 



