Page:Popular Science Monthly Volume 46.djvu/254

242 Island, the widespread view of sea and land impresses itself upon the observer, and in every way in which this range of hills is brought to our notice we are unconsciously led to appreciate the scenic importance of this legacy of the continental ice sheet.

From the scenery of Long Island Sound and the moraine one may turn to that of the Hudson River.

On the east shore of this noble stream is a terrace, picturesquely dotted with handsome country seats, which extends almost continuously from New York to Peekskill, and, after a brief interruption where the steep slopes of Anthony's Nose and the Dunderberg form the lower gate of the Highlands, reappears at Garrison's and Cold Spring and forms the plain upon which the Military Academy is located, at West Point, This terrace is about seventy-five feet above tide at the Riverside Park in New York city, and increases in height northward to about one hundred and twenty feet at the State Camp near Peekskill and one hundred and eighty feet at West Point. North of the Highlands the remnants of terraces may be seen on both shores of the river as far as Troy and throughout the valley of Lake Champlain, increasing in height northward to the St. Lawrence River, where, in the vicinity of Montreal, they have an altitude of over five hundred feet.

In these terraces is recorded ineffaceably the history of the continental submergence previously mentioned. They are the remnants of the deposit of sand and clay formed in the Hudson and Champlain Valleys when submerged, and the surface of the highest terrace indicates approximately the old sea level.

These terraces, relics of Quaternary subsidence, are not, however, the only interesting geological phenomena to be seen along the valley of the Hudson. The bold, precipitous Palisades, known as widely as the river which they overlook, call our attention to a period of volcanic activity in Mesozoic time. These lofty cliff's form the margin of a sheet of trap or igneous rock, three hundred to four hundred feet in thickness, which was forced to the surface in a molten state between the beds of red Triassic sandstone which form the eastern border of northern New Jersey and of Rockland County, New York.

Throughout most of its extent the Palisade range has been leveled off by wave action at some remote period of subsidence, while immediately west and north of Nyack a portion which has escaped erosion rises in high peaks with irregular outlines.

Leaving the Palisades behind us, we enter the gorge of the Highlands. The rocks which form these rugged steeps are of the oldest and hardest in our State. Though they have yielded to the cutting of the river current in past ages, they resist the