"Montrose to Cornwall. This celebrated passage of the Hudson through the Highlands, is a gorge nearly 20 miles long from 3 miles south of Peekskill to Fishkill, and is worn out of the Laurentian rocks far below mean tide water. The hills on its sides rise in some instances as much as 1,800 feet, and in many places the walls are very precipitous. The rock is gneiss, of a kind that is not easily disintegrated or eroded, nor is there any evidence of any convulsive movement. It is clearly a case of erosion, but not by the present river, which has no fall, for tide water extends 100 miles up the river beyond the Highlands. This therefore was probably a work mainly performed in some past period when the continent was at a higher level. Most likely it is a valley of great antiquity. "Opposite Fishkill is Newburgh, which is in the great valley of Lower Silurian or Cambrian limestone and slate. North of that, on the west side of the river, the formations occur in their usual order, their outcrops running northeast and southwest. On the _N. Y. C. & H. R. R. R._, on the east side, the same valley crosses, and the slates from Fishkill to Rhinebeck are about the same place in the series; but being destitute of fossils and very much faulted, tilted and disturbed, their precise geology is uncertain. See the exposures in the cuts at Poughkeepsie. The high ground to the east is commonly called the Quebec group. * * * Amid thy forest solitudes one climbs O'er crags, that proudly tower above the deep, Along the verge of the cliff, and he can hear The low dash of the wave with startled ear. _Fitz-Greene Halleck._ * * * "A series of great dislocations with upthrows on the east side traverse eastern North America from Canada to Alabama. One of these great faults has been traced from near the mouth of the St. Lawrence River, keeping mostly under the water up to Quebec just north of the fortress, thence by a gently curving line to Lake Champlain or through western Vermont across Washington County, N. Y., to near Albany. It crosses the river near Rhinebeck 15 miles north of Poughkeepsie and continues on southward into New Jersey and runs into another series of faults probably of a later date, which extends as far as Alabama. It brings up the rocks of the so called Quebec group on the east side of the fracture to the level of the Hudson River and Trenton. "Catskill Mountains. For many miles on this railroad are beautiful views of the Catskill Mountains, 3,800 feet high, several miles distant on the opposite or west side of the river, and which furnish the name for the Catskill formation. The wide valley between them and the river is composed of Chemung, Hamilton, Lower Helderberg and Hudson River. The geology on the east or railroad side is entirely different.