In addition to various geological references
scattered through these pages the following facts from an
American Geological Railway Guide, by James Macfarlane,
Ph.D., will be of interest.
"The State of New York is to the geologist what the Holy Land is to the Christian, and the works of her PalŠontologist are the Old Testament Scriptures of the science. It is a Laurentian, Cambrian, Silurian and Devonian State, containing all the groups and all the formations of these long ages, beautifully developed in belts running nearly across the State in an east and west direction, lying undisturbed as originally laid down.
"The rock of New York Island is gneiss, except a portion of the north end, which is limestone. The south portion is covered with deep alluvial deposits, which in some places are more than 100 feet in depth. The natural outcroppings of the gneiss appeared on the surface about 16th Street, on the east side of the city, and run diagonally across to 31st Street on 10th Avenue. North of this, much of the surface was naked rock. It contains a large proportion of mica, a small proportion of quartz and still less feldspar, but generally an abundance of iron pyrites in very minute crystals, which, on exposure, are decomposed. In consequence of these ingredients it soon disintegrates on exposure, rendering it unfit for the purposes of building. The erection of a great city, for which this island furnishes a noble site, has very greatly changed its natural condition. The geological age of the New York gneiss is undoubtedly very old, not the Laurentian or oldest, nor the Huronian, but it belongs to the third or White Mountain series, named by Dr. Hunt the Montalban. It is the same range which is the basis rock of nearly all the great cities of the Atlantic coast. It crosses New Jersey where it is turned to clay, until it appears under Trenton, and it extends to Philadelphia, Baltimore, Washington and Richmond, Va., and probably Boston, Massachusetts, is founded on this same formation.
"On the opposite side of the river may here be seen for many miles the Palisades, a long, rough mountain ridge close to the water's edge. Its upper half is a perpendicular precipice of bare rock of a columnar structure from 100 to 200 feet in height, the whole height of the mountain being generally from 400 to 600 feet, and the highest point in the range opposite Sing Sing 800 feet above the Hudson, and known as the High Torn. The width of the mountain is from a half mile to a mile and a half, the western slope being quite gentle. In length it extends from Bergen Point below Jersey City to Haverstraw, and then westward in all 48 miles, the middle portion being merely a low ridge. The lower half of the ridge on the river side is a sloping mound of detritus, of loose stones which has accumulated at the base of the cliff, from its weathered and wasted surface.
"Viewed from the railroad or from a steamboat on the river, this lofty mural precipice with its huge weathered masses of upright columns of bare rock, presenting a long, straight unbroken ridge overlooking the beautiful Hudson River, is certainly extremely picturesque. Thousands of travelers gaze at it daily without knowing what it is. This entire ridge consists of no other rock than trap traversing the Triassic formation in a huge vertical dike. The red sandstone formation of New Jersey is intersected by numerous dikes of this kind, but this is much the finest. The materials of this mountain have undoubtedly burst through a great rent or fissure in the strata, overflowing while in a melted or plastic condition the red sand-stone, not with the violence of a volcano, for the adjoining strata are but little disturbed in position, although often greatly altered by the heat, but forced up very slowly and gradually, and probably under pressure. Subsequent denudation has laid bare the part of the mountain now exposed along the river. The rock is columnar basalt, sometimes called greenstone, and is solid, not stratified like water-formed rocks, but cracked in cooling and of a crystalline structure. Here is a remarkable but not uncommon instance of a great geological blank. On the east side of this river the formations belong to the first or oldest series of Primary or Crystalline rocks, while on the west side they are all Triassic, the intermediate Cambrian, Silurian, Devonian and Carboniferous formations being wanting. This state of things continues all along the Atlantic coast to Georgia, the Cretaceous or Jurassic taking the place of the Triassic farther south.
"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.
"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.
"Albany. The clay beds at Albany are more than 100 feet thick, and between that city and Schenectady they are underlaid by a bed of sand that is in some places more than 50 feet thick. There is an old glacial clay and boulder drift below the gravel at Albany, but Professor Hall says it is not the estuary stratified clay."
(Condensed from article by permission of writer.)
The tide in the Hudson River is the continuation of the tide-wave, which comes up from the ocean through New York Bay, and is carried by its own momentum one hundred and sixty miles, growing, of course, constantly smaller, until it is finally stopped by the dam at Troy. The crest of this wave, or top high water, is ten hours going from New York to Troy. A steamer employing the same time (ten hours) for the journey, and starting at high water in New York, would carry a flood tide and highest water all the way, and have an up-river current of about three miles an hour helping her. On the other hand, the same steamer starting six hours later, or at low tide, would have dead low water and an ebb tide current of about three miles against her the entire way. The average rise and fall of the tides in New York is five and one-half feet, and in Troy, about two feet.
Flood tide may carry salt water, under the most favorable circumstances, so that it can be detected at Poughkeepsie; ordinarily the water is fresh at Newburgh.
To those who have not studied the tides the following will also be of interest.
The tides are the semi-diurnal oscillations of the ocean, caused by the attraction of the moon and sun.
The influence of the moon's attraction is the preponderating one in the tide rising force, while that of the sun is about two-fifths as much as that of the moon. The tides therefore follow the motion of the moon, and the average interval between the times of high water is the half length of the lunar day, or about twelve hours and twenty-five minutes.