180 Association of American Geologists and Naturalists. 



Prof. H. D. Rogers presented some details in. relation to the 

 striated surfaces of the northeastern counties of Pennsylvania, 

 and the adjacent districts of New York, proving that while the 

 scratches which abound on the summits of all the mountain 

 ridges in that part of the Appalachian chain observe a nearly 

 north and south direction, answering to their prevailing course 

 throughout New England and the country of the lakes, those on 

 the sides and bottoms of the valleys, obey with remarkable 

 fidelity all the local deflections which a body of moving waters 

 would encounter among the ridges and valleys of this entangled 

 range. In the neighborhood of the Wyoming valley, the sum- 

 mits of the mountains, elevated about two thousand feet above 

 the sea, and one thousand five hundred above the valley, are 

 covered with nearly parallel strise, pointing a little west of south, 

 but on their slopes, in the bed of the valley, these lines fol- 

 low other directions conforming to the course which any ob- 

 structed inundation would pursue. Thus, near Wilkesbarre, 

 the northern flank of the southern mountain, which was here ex- 

 posed to the full brunt of the inundation, exhibits the grooves 

 with a direction compounded of the general meridional one, and 

 that of the deflecting mountain wall. High on the side of the 

 ridge, the striae ascend the slope obliquely, but nearer the base 

 they are parallel to the medial axes of the valley. Near the la- 

 teral notch, in the northern mountain at Nanticoke, they point 

 toward the gorge, showing that a portion of the current here 

 came from a quarter south of east. A great northern wave 

 would, so long as it submersed in its first impetuous rush the 

 summits of the mountains, move forward regardless of the local 

 inequalities of the surface, but after it had partially subsided, the 

 long parallel ridges would present so many barriers to divide and 

 locally deflect the now feeble remnant of the drainage. Review- 

 ing the phenomena which he has observed, Prof. Rogers con- 

 cludes that the strias were produced by the friction of the over- 

 lying stratum of drift itself, urged into rapid motion from the 

 north by one or more sudden inundations. ' From the absence 

 near the southern border of the striated region of granitic, or 

 other far transported northern bowlders, he infers that floating 

 ice, while it may have been concerned in dispersing the detrital 

 matter from the north, has had no agency in furrowing and 

 smoothing the surfaces of the strata. 



