Much has been said, filmed, recorded, and written about High Tor Mountain since it was first spotted by Henry Hudson’s crew (and before that, maybe Verazzano’s crew, and before that Native Americans. . .). High Tor Mountain is the crowning peak of the Palisades Escarpment, the network of volcanic rock cliffs and peaks that extends from Staten Island to Pomona, New York – a 30-mile stretch. Most iconic are the vertical cliffs of the New Jersey side of the Hudson River, which begin in Hoboken and continue nearly to Sneden’s Landing and Piermont.
The cliffs were named by Verazzano’s crew as ‘Palisades,’ or “fence of stakes,” which was indicative of the forts built by local Native Americans. I would argue that the Native Americans, at the time, did not construct palisade walls, as this was originally a Roman tradition that was passed on to the Celts, Normans, and other Northern Europeans. Verazzano was merely describing the walls of forts he had seen on the remains of battle fields in Europe. Imagine a frontier outpost built of hacked logs, vertically buried in the ground, with the tops whittled to spikes – the spiked logs make a wall that is seemingly impenetrable. The Palisades really do resemble a palisade wall.
The United States Geological Survey (USGS) reveals much information on the Palisades Escarpment at its website: http://3dparks.wr.usgs.gov/nyc/parks/loc39.htm . The website says:
The Palisades were designated a “National Natural Landmark” being “the best example of a thick diabase sill in the United States.” The sill extends southward beyond the cliffs in Jersey City beneath the Inner Harbor, and reappear on Staten Island (see Figure 24 on the Staten Island page). The Palisades are the eroded cross-section of a large intrusive diabase sill that intruded between layers of sandstone and shale of the Late Triassic Stockton and Lockatong Formations. (In the Staten Island area, the strata equivalent to the Lockatong Formation is called the Brunswick Formation.) The sill approaches 1,000 feet thick and was probably fed from an unknown stock buried beneath the basin to the west. Radiometric age determinations of the diabase suggest that the sill formed in multiple stages between about 192 to 186 million years ago (late Early Jurassic). Exposures of the basal chill zone, a zone of contact metamorphism of the underlying sedimentary layers, occur scattered amongst the massive talus slopes at the base of the cliff. The upper side of the sill also has a chill zone with the upper part of the sill displaying many xenoliths (pieces of the overlying host rock in which the sill intruded). Within the lower portion of the sill there is a zone of rock enriched in olivine, a high temperature ultramafic mineral that formed first and settled to the bottom of the intrusion before the rest of the magma cooled. This zone is about 10 to 15 feet thick, and crops out along and above the road in the Ross Dock area near the south entrance to the park (see Figure 89).
The escarpment of the Palisades reveals the strike of the eastern margin of the Newark Basin. The path of the Hudson River follows the trace of the underlying unconformity at the base of the Stockton Formation (see Figure 88 on the Newark Basin page). This unconformity represents the gentle ancient landscape surface that existed in the region before rifting occurred. As continental glaciers scoured the lower Hudson River Valley, the softer sedimentary cover above this unconformity was preferentially stripped away. In addition, during low-standing sea level, the Hudson River also preferentially followed this boundary.
In a documentary I watched recently (“How the Earth Was Made”), the Palisades Escarpment is described in an exciting light. At the dawn of the age of Pangea (when all the continents were “one” amidst a massive ancient sea), plate tectonics began to rip apart the continent. At this time (over 200 million years ago), it is thought, what is now New York City was literally at the center of the world. The plates began to move in their respective eastern or western directions and magma began to pour out of the earth at this massive rift (now the continental divide at the bottom of the Atlantic Ocean). The molten rock covered an area the size of Australia and was, at times, nearly a half mile thick. Imagine a massive ocean of liquid rock, churning and flaring off super heated gases. The magma also found its way into ancient, horizontal sandstone and shale fissures. The underground flowing magma “river” created what is known as a sill, buried beneath layers of sandstone and shale. The Palisades Interstate Park Commission dedicates a website to this phenomenon, and describes the process of sill formation (the website describes the process as taking place within a “day,” but this is actually stretched of hundreds of millions of years):
It literally bakes the rocks with which it comes into contact, metamorphosing some of them into the red, crumbly stone one still finds beneath the ancient sill (good examples of this metamorphic rock, “baked” shale, can be found behind the Kearney House).
. . . the sill cools and hardens beneath the ground, the molten rock crystallizing into the hard Palisades stone called diabase.Still well before “dawn,” further convulsions caused by the breakup of Pangea result in the entire region being shifted down between 17 and 20 degrees to the west, lifting the eastern edge of the hardened sill (that raised edge will become the Palisades Cliffs).
Throughout the course of the rest of the “day,” as the pieces of Pangea slowly move into the positions of the continents as we think of them, the forces of erosion—wind and rain, streams and gravity—will relentlessly whittle away at the softer stone above and around the buried sill. Little by little, parts of the buried sill, especially along its easternmost, raised edge, begin to emerge above the surface. (Just as a point of reference, it is believed that at around 4:30 in the “afternoon,” i.e., about 65 million years ago, a meteor or comet slams into what is today the Yucatan Peninsula; the global winter created by this event will spell the doom of the dinosaurs, the ascendancy of mammals.) An ancestral stream flowing roughly along the path of today’s Hudson also does its part to chisel away the softer stone to reveal more of the edge of the sill. By “dinnertime,” the continents are more or less in their present positions. (Around “11 pm,” meanwhile, the earliest ancestors of human beings show up in Africa…)
Throughout the “evening,” the creatures living here in the future New York–New Jersey metropolitan area enjoy a subtropical climate. Then, a “minute” or two before the end of our “day,” a series of Ice Ages overtake the earth. The causes of these dramatic global shifts in climate are not yet well understood, even if the results are. As temperatures drop in the north, snow fails to melt in places it previously had. Winter after winter, new snow piles upon the old, until that pile grows to hundreds of feet tall. Its own weight compresses the snow at the bottom of the pile, until it begins to behave like something other than snow. It begins to behave like a liquid.
It begins to flow.
Moving in the path of least resistance—generally, south in this hemisphere—the massive pile of frozen snow and ice begins, in essence, to smoosh itself across the ground before it. A glacier has been born. Slowly—its progress typically measured in feet, even inches, per year—this frozen mass of water grinds over the surface of the earth, scraping away anything loose in its path. Vegetation, even mighty forests, loose stone, soil—all of it gets inexorably pushed in front of the plough of the glacier. Called moraine, this line of debris will be left behind when the glacier finally begins to melt back (or, retreats), a deep pile of rubble, called terminal moraine, which marks the southernmost reach of the glacier’s leading edge. In the case of the last (or, perhaps better put, most recent) glacier, the Wisconsin Ice Sheet, its terminal moraine is found as far south as Newark, New Jersey; much of the high ground in Long Island is likewise made up of terminal moraine from the Wisconsin Ice Sheet. Within the terminal moraine, no doubt, are vast quantities of the sandstones and shales that once encased the Palisades. Also, there are pieces of the sill itself in the terminal moraine, the “talus” that had fallen from the cliffs before the glacier came. The cliffs, in other words, are when the glacier retreats as sheer from top to bottom as they ever will be; new talus will begin to accumulate at their base.
Now it is a few “seconds” before “midnight.”
As the glacier continues to retreat (along its retreat route it will scatter boulders that failed to dislodge at its terminus; these are called erratics), the first human beings arrive on the scene, hunters and gatherers of the forests and wetlands that emerge as the ice slowly returns north.
(Again for point of reference: a Florentine navigator named Verrazano will make the first written record of the Hudson in 1524, almost four centuries ago—and just inside of a quarter of a second before the final “midnight” of our peculiar “day”…)
Most scientists who study climate believe that we are most likely in what is termed an “interglacial period”—between two Ice Ages. (The next Ice Age, however, remains most likely millennia in the future; and, of course, there is the ongoing debate about the effects that human activity may have on climate.) Yet even without a glacier bearing down upon us, ice continues to be a powerful shaper of the Palisades.
When the diabase cooled, it naturally formed into vertically arranged columns, the tall pillars of rock that gave the cliffs their name (they reminded someone of a palisade-type stockade fence). The cliff face and its columns are rife with cracks. Into these cracks each year rainwater collects. In the winter, that water freezes. Water, unlike any other substance on earth, expands when it freezes. (The same property causes ice cubes in a freezer tray to rise above the rim.) That expansion can exert a force on the order of 2,000 pounds per square inch. This force in turn enlarges fissures in the rock face and can result in rockslides, though often they occur months after the spring thaw.
It all reminds us in a way of the childhood game of Paper, Scissors, Rock—except, in this version, Water, especially in its frozen form, usually wins…
It is said that there are “sisters” to the Palisades Escarpment that can be found in west Africa, the Atlantic coast of the United Kingdom, and parts of the Brazil coast. Our geology is literally scattered across the shores of the Atlantic, as these pieces were once united during the time of the dinosaurs.