440 JULIEN 



Island, a remnant of the same rocks survives, penetrated by the 

 same intrusive sheets of pegmatite and diorite, and they may 

 underHe the island beyond. To the south, the submarine 

 course of the buried channel of the Hudson river reaches for 

 120 miles, with a topographical uniformity which suggests 

 erosion of the same class of rocks in that direction. On the 

 southwest and west, the same gneisses, amphibole schists, ser- 

 pentine and granite outcrop along the shore for over ten miles, 

 on a probable westward extension of the same formation into or 

 across New Jersey. The eruptive tract on Manhattan Island 

 thus forms the center of a vast region of sharply folded, crys- 

 talline schists, now degraded toward a base level, whose area, 

 largely that of the base of Mount Manhattan, stretches over 

 hundreds of square miles. 



The survival of the remaining portion of these ancient schists 

 above the sea-level has been due only in part to the highly tilted 

 position of the layers, offering but their edges to attack by 

 agencies of erosion and decay. Almost every knoll upon the 

 island and even the long ridges, reaching i 50 to 200 feet in 

 altitude, such as Morningside Heights, Washington Heights, 

 and the heights of Inwood, are capped or seamed by sheets of 

 igneous intrusions of both classes, or even so saturated with 

 pegmatite lenses as to have become consolidated into a granite 

 mass. The resistance and protection thus afforded to the sur- 

 rounding schists are attested by these hard bands and rounded 

 hummocks, gnawed and scored by the teeth of the Great 

 Glacier, and have preserved the varied topography of this 

 exposed rocky promontory in preparation for the beautiful 

 site of the great city. 



But the peak of Manhattan was but one of many which 

 crowned the mountain wall stretching from southwest to north- 

 east along the old coast, and which call for designation, for 

 convenient reference. 



The lofty crest, with volcanic vent, on the site of Wilmington, 

 Delaware, may be indicated by the original Indian name of that 

 locality,^ as Mount HopokaJiacking. 



^ I. Acrelius, A History of New Sweden, Philadelphia, 1874, 24. 



