treme end of the island, succumb to the picturesque ledges of gneiss at Spuyten Duyvil Creek.
If
now we suddenly transport ourselves to the east side of the island and
continue a survey southward, we find in Harlem, in the latitude of
Randall's Island, traces of such hummocks and hills of drift as
characterized the region south of 23d Street; while beginning at 89th
Street, opposite the slim tip of Blackwell's Island, we encounter a rim
or ledge of rock, sometimes precipitous and again retreating,
continued south toward 50th Street the basement of a meridional ridge,
or one running north and south, like those we have encountered,
somewhat en echelon, on the west.
Gathering
together the results of such a topographical sketch, and eliminating
simply varietal features, we find Manhattan Island to be a ridge,
generally rising ia elevation towards the north, sinking towards the
south, where its rocky floor has disappeared below the mantle of
superficial detritus, drift and sediments piled up over it and broken
up into north and south alignments of hills, intersected and
diversified by flats, valleys, passes and ravines, and again revealing
broad undulations which cross them transversely, somewhat irregularly
related to the north and south lines, but still unquestionably present
at Murray Hill, the fold at 59th and 93d Streets, Cathedral Plateau and
Hamilton Grange. There is also quite discernible a shifting westward of
the highland towards the channel of the Hudson, leaving a bay and
semi-estuarine level, on the east at the junction of the Harlem and
East River channels and the Sound, with, however, rocky prominences on
the west, immediately or almost in contact with the East River below
98th Street.
Two
water channels deeply excavated in rocky basins bound it on the east
and west, and two notable depressions, those of Manhattanville and
Inwood, cross it obliquely, while a gash, or fault, at Spuyten Duyvil,
subsequently eroded into a waterway, separates it from identical
formations to the north. Its present features are doubtless due to
comparatively modern
