1895.] NATURAL SCIENCES OF PHILADELPHIA. 203 



Gap up with ice but moved diagonally across it." Glacial stria' all 

 pointing in a direction obliquely across the mountain and the Gap, 

 occur at various heights and on the top of the mountain, but no 

 striae were noted below the Kittatinny House. This hotel stands 

 upon the 120 foot contour line of Chance's map, though according to 

 Mr. Erodhead it is 180 feet above the river and is situated just be- 

 low the north entrance to the Gap. 



Above the carriage road, on the Pennsylvania side, not far from 

 the narrowest part of the gorge, a series of beautiful, polished, hori- 

 zontal grooves of considerable size may be seen ; on the perpendicular 

 face of the sand-stone rock, Mr. L. W. Brodhead gives the height 

 of these grooves above river as 150 feet. Their course is nearly at 

 right angles to the direction of the glacial stria? on the mountain. 



Whether these are glacial grooves, or whether they are, as seems* 

 to me most probable, the result of a swift current of water carrying 

 much debris, they certainly show that a powerfully erosive agent of 

 some kind passed through the Gap at about the height of 150 feet. 

 Now at this same height stands the upper terrace of the present river, 

 while not far above the same elevation lies the old river gravel, and 

 glacial striae appear to be absent below a nearly equal level. The 

 position of grooves, terrace, old river gravel and absence of glacial 

 stria?, so nearly on the same line, is explained, if the rock wall of 

 the centre of the amphitheatre stood somewhere near a height of 150 

 feet at the end of the Ice Age. 



When the water commenced to tlow over this rock-wall it would 

 begin the cutting of the short lower, or south portion of the Gap. 

 Its walls are very precipitious for a short distance and the gorge 

 ends rather suddenly, as the southeastern face of the Kittatinny 

 Mountain is exceedingly bold. This lower gorge extends from the 

 Point of Rocks to the head of the rapids over the Hudson River 

 slates. The width of the channel where the river passes from the 

 upper gorge to the lower, as before stated, is 400 feet, but it increases 

 to 800 feet at its wide- spreading mouth. This very rapid curving 

 outward of the walls of the lower gorge, on both sides of the river 

 so nearly alike, seems to indicate the impetuous rush of an immense 

 body of water. 



The difference in the character of the bed of the present river 

 from Port Jervis to the beginning of the Hudson River slates 

 and from the beginning of the Hudson River slates to the 



