AN AMERICAN GEOLOGICAL RAILWAY GUIDE. (X.Y.) 



perhaps mountains to be overcome, as they are everywhere from the Mohawk Valley to Alabama. 

 if even the limestone ridge of the Helderberg range, which bounds this valley on the south, had taken 

 a northern direction, as the 2-4. Cambrian formations do, a tunnel would probably have been 

 necessary. In the western part of the State these Helderberg limestones continue, but not as a 

 prominent ridge. The road via Geneva, runs on them at Auburn, Clifton Springs, &c., but with 

 less favorable grades than the direct road, and at Buffalo they are level with the plain. It should 

 be added that the old Laurentian mountains at Little Falls and at Peekskill have been cloven from 

 top to bottom, thus opening the gateways for the traffic and travel of the West. The popular 

 impression that New York is a level plain like the prairies of the West, derived from traveling on 

 the N. Y. C. & H. R. R. R., is altogether erroneous. There is only a narrow trough through the 

 centre of the State, in which the railroad and canal are located, that is of this level character. 



4. New York island is 12 miles Ions and nearly 2 miles wide. The widest point is two and one- 

 quarter miles at 14th St. Below Grand street it gradually becomes narrower as well as at the north 

 end. The lower part of the city, below Wall street, is half a mile wide. The rock of the 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 

 outcropping 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 1 a. Laurentian or oldest, nor the 1 b. Huronian, but it 

 belongs to the third or White Mountain series, named by Dr. Hunt the 1 c. 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. 



5. 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 1011 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, being derived from its weathered and 

 wasted surface. This talus and the summit of the mountain are covered with trees, with the 

 bare rocky precipice called the Palisades between, and many fine country residences may be 

 seen on the level summit, from which are beautiful views of the river, the harbor and City of 

 New York. 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 16. 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 sandstone, 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. (See description of the 

 16. Triassic formation and its Trap Dikes). Here is a remarkable but not uncommon instance of a 

 great geological blank. On the east side of this river the formations belong to No. 1, the first or 

 oldest series of Primary or Crystalline rocks, while on the west side they are No. 16, all the 

 intermediate Cambrian, Silurian, Devonian and Carboniferous formations being wanting. This 

 state of things continues all along the Atlantic coast to Georgia, the 18. Cretaceous or 17. Jurassic 

 taking the place of the 16. Triassic farther south. 



6. 38 Montrose to 54 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 1 a. 

 Laurentian rocks far below mean tide water. The hills on its sides rise in some instances as much 



