Standing on the shore halfway down the length of Ballston Lake with a young research assistant named Devin Delevan, I suppose I could be forgiven for mistaking the lake for a river: It is obviously a great deal longer than it is wide, though it shows little of the bending that any proper river should exhibit as it follows the lay of the landscape.
The false impression is quickly dispelled with a glance at a map of the region, for it can easily be seen that the lake lies in a narrow valley, fed mainly by local runoff and some small feeder streams, and empties into the rather unimpressive Ballston Brook as its waters make their way via Round Lake to the Hudson River.
Long, narrow, straight lakes are common in areas that once lay under glaciers. Throughout the Adirondacks, melting glaciers left water in fault valleys called “grabens” that are partially dammed up by the glacial sediment known as moraine. The Ausable Lakes, the Cascade Lakes, and Lake George are impressive examples.
But Ballston Lake has a different history. Thousands of years ago, highly energetic waters of the ancient Mohawk River flowed through the valley now occupied by Ballston Lake. But the river abandoned the valley, leaving the quiet lake as a reminder of how the melting Continental glacier altered the landscape of New York State.
Envisioning the ancient past
In nearly every geology course I have taken, students have been told by the professor that to truly understand historical geology one must have a good imagination: To envision, for example, this part of North America during the Devonian period, 400 million years ago, when it lay under a warm, shallow sea; or during the Mesozoic Era when dinosaurs roamed the lands that would become New York and New England, leaving their bones in sediments-turned-to-rock that have almost entirely been eroded away, except for a few places such as the Connecticut River valley; or the end of the Great Ice Age, some 15,000 years ago, when the northern parts of New York State still lay deeply buried under the steadily retreating edge of the Continental ice sheet.
But, at that time, the whole upper half of the country was coming out of the last great advance of the ice, leaving much of the Midwest flowing with rivers and streams from the melting glacier, many of them now shrunken or vanished entirely. A map of the Midwest then would look very different from the way it looks now, for the present Great Lakes had not yet formed.
Instead, the basin in which Lake Ontario sits was occupied by a much larger body of water that geologists call Lake Iroquois, which derived some of its water from proto-Lake Erie and from a huge lake farther west known to geologists as Lake Alqonquin, which would eventually evolve into Lake Huron.
Today, the Great Lakes drain into Lake Ontario via Lake Erie — and Niagara Falls — and thence into the St. Lawrence River en route to the Atlantic Ocean. But, in those ancient times, what would eventually be known as the St. Lawrence River Valley was under a mile or more of ice, and the massive Continental glacier blocked melt water from flowing directly to the ocean.
Hence, the water found its way through the ancient form of today’s Mohawk River, a river vastly more voluminous and powerful than its relatively placid modern descendant.
Today the Mohawk’s source is considered to be Lewis County, but, around 13,500 years ago, it carried the waters of Lake Iroquois, which seems to have undergone what geologists call “catastrophic” drainage. This likely was caused by the rupture of an extensive ice dam, and the turbulent flood waters cut a broad valley across the middle of New York State.
The steep cliffs that tower over the Mohawk west of Amsterdam and the wide, deep potholes that are cut into the bedrock of its banks in many places testify to the volume and power of its surging waters. And the Mohawk today — along with many other streams scattered across the northern part of the continental United States — is classified as an “under-fit” stream, meaning, simply, that it is but a remnant of its former identity as a voluminous, highly erosive river.
Evidence of this fact is easily visible to motorists on the Northway. About a mile south of Exit 12, drivers pass through a broad, deep valley that stretches east toward the Hudson River and west toward Ballston Lake. On its north side are visible once-rugged cliffs that are now softened by years of erosion and tree growth. At the bottom of the valley flows only the gentle Ballston Brook, offering barely a hint of the great and powerful flow that once cut down through the bedrock.
Where did the river go?
But this scene triggers the question: Where did the river go and why did it go there?
The answer, as with many geologic questions, lies in the distant past. As the Continental glacier retreated from New York State nearly 15,000 years ago, the Hudson River Valley — which carried an enormous volume of the glacial melt water — became blocked somewhere near Newburgh.
The blockage was presumably made of moraine and it formed a gigantic natural dam. Its effect was to create to its north an extensive body of water known to geologists as Glacial Lake Albany. The lake stretched at least as far north as Glens Falls, and probably resembled Lake George and Lake Champlain, both of which were left by the retreating glaciers.
To the north of the natural dam, the east and west sides of the Hudson Valley have fairly steep profiles until the Albany area is reached, which kept the lake relatively confined and narrow. But, at Albany, the west side becomes a broad, gentle upward slope, and so the lake was at its widest in the Albany-Schenectady-Troy area, stretching east on a line that probably closely followed today’s Route 4 — only a couple of miles from the river — but west as far as Schenectady.
This meant that the Mohawk River — which at that time was carrying massive volumes of water and sediment from western New York State and the proto-Great Lakes — did not become a tributary of the swiftly flowing Hudson as it is today above Cohoes but was a standing body of water. And, when rivers do this, they slow down and begin to deposit their massive loads of sediment. The result is the development of a delta.
For examples, think of the Mississippi Delta or the delta of the Nile River. The Pine Bush of Albany County formed, and numerous sandy pine barrens to the north of Albany along today’s Hudson River show the presence of other, smaller interlocking deltas as well.
Within deltas, rivers break up into what are called “distributaries” — networks of lacy, interwoven smaller streams and perhaps two or more larger ones. Given the vagaries of seasonal changes in the volume of water and sediment being transported, these distributaries are subject to sudden, rapid changes in their paths.
At some point in the distant past, a distributary of the ancient Mohawk found its way into the valley that today holds Ballston Lake, and the cliffs in the lower part of the valley testify to its erosive power. But as the Continental ice sheet retreated farther and farther to the north, the St. Lawrence Valley became ice-free and, as the volume of water in the proto-Great Lakes decreased, it was able to find its way to the Atlantic Ocean through that newly exposed, lower-elevation channel.
The distributary of the Mohawk that flowed through the area now occupied by Ballston Lake was deprived of its major source of recharge, and the lake was left behind as a remnant of its once-significant role in the drainage patterns of New York State.
So, the next time you are headed up the Northway — take a moment as you approach Exit 12 and observe the valley over which the road crosses. Let your imagination carry you back 15,000 years and picture a powerful river sweeping down from the west, carrying with it melt water and sediments from the vast retreating ice sheet, bound for the great body of water called Glacial Lake Albany.
If you can envision them, perhaps a herd of wooly mammoths or a mastodon or two may lumber aside the rushing waters: This was New York State in the twilight of the Great Ice Age.
Though it lies a scant two-and-half hours east of Albany via Route 7 in New York State and routes 9 and 101 in Vermont and New Hampshire, Mount Monadnock is probably not well known to anyone locally who is not a hiker. Though its presence looms in the dialogue of Thornton Wilder’s classic play Our Town — set in the fictional village of Grover’s Corners, modeled on the New Hampshire town of Jaffrey — it is hardly a household name such as iconic Northeastern peaks like mounts Marcy or Washington.
But, over the last century or so, Mount Monadnock has lured millions of hikers to its summit; according to various websites, it may be the second-most-frequently climbed mountain in the world. The first is Mount Fuji in Japan with sacred slopes that draw pilgrims and outdoor enthusiasts from all parts of the globe. But, since cities such as Albany, Boston, Worcester, Hartford, and Providence as well as a great many colleges with outing clubs, are located within a couple of hours’ drive from the mountain, on a nice day almost any time of the year there may be upwards of a hundred people on the peak at mid-day.
It may be crowded, but at least climbers will not be approached by visitors who have driven up and will look at them with a mixture of awe and condescension and ask, “Did you walk up here? Didn’t you know there was a road?” Because there isn’t one!
The name “Monadnock” — “Mon-ADD-nock” seems to be the preferred pronunciation — is derived from the Native American Indian Abenaki language: menonadenak, meaning "smooth mountain," or menadena, meaning “isolated mountain.”
This latter translation is the one that has been adopted by geologists to refer to any prominent mountain or erosional remnant that rises in lonely isolation from a much flatter landscape. In Schoharie County, the volcanic-looking hill known as “Barrock Zourie” — easily visible from Route I-88 — is another example of a monadnock — with a lower-case “m.”
Despite its appearance, Barrock Zourie is not a volcano; it is a lone remnant of what was once a much higher, more extensive part of the Cobleskill Plateau, composed of alternating layers of shale and sandstone laid down during the Devonian time, some 400 million years ago.
New Hampshire’s eponymous Monadnock, however, does contain intrusions of granite — an igneous rock — but it is not volcanic either. The bedrock of Mount Monadnock began to form 400 million years ago when that part of the United States and the Helderberg area were under a warm shallow sea, undoubtedly resembling today’s Bahamas as can be determined by its fossils: corals, sea stars, sea “lilies” (actually animals), and various shellfish.
But great changes were on the way. To the east was an ancient continent known as “Avalonia,” which comprises today’s western Europe and parts of the Atlantic coast of North America. Through the relentless forces of plate tectonics, Avalonia and the landmass that would some day be North America were being driven together, headed eventually for a massive, bedrock-scrunching collision known as the Acadian Orogeny, or “mountain building episode.”
To understand what resulted, think what would happen if the fronts of two cars were to collide at something of an angle in a parking lot. Their hoods would be crushed and distorted and probably forced upwards at jagged angles. This is a very simplified analogy to events during the Acadian Orogeny.
As Avalonia and proto-North America collided, the bedrock along their margins was subjected to massive earthquakes and distortions such as folding. The sediments that had once lain under the sea were subjected to heat and pressure, forcing massive amounts of materials to undergo metamorphism; hence the layers of shale and sandstone were compressed and cooked over millions of years into the metamorphic rock known as schist, sometimes laced with veins of quartz and graphite and more exotic minerals such as garnet.
The great subterranean heat also brought upwards injections of magma that cooled over long periods of time into the common igneous rock granite, which in places metamorphosed into gneiss. And so the materials of Mount Monadnock were formed and pushed skyward — perhaps to lofty Himalayan heights.
But the in the millions of years since their birth, the once towering Acadian Mountains have been reduced in elevation and mass by the agents of weathering and erosion; however, rugged summits such as Mount Washington and some other of the White Mountains farther north in New Hampshire and craggy Mount Katahdin in Maine — all of them approaching or exceeding a mile in height — offer daunting challenges to climbers.
Still, these peaks are part of massifs — a French term referring to extensive regions of high mountains. Mount Monadnock, on the other hand, is but a remnant of what was also once an extensive massif, much of which still exists in the form of the White Mountains
Monadnock towers above a domestic landscape of low, rolling hills, placid ponds and lakes, meandering streams and the long, narrow glacially deposited hills called “drumlins.” As such, it seems exceptionally prominent, especially given its bare, windy summit with its massively fractured cliffs, towering above its tree-clad lower slopes.
There are a number of routes to that summit, all of which wander in and out of lush forests of hardwoods and fragrant firs, from time to time breaking out onto rocky, glacially polished ledges offering stunning views of the summit and of the surrounding countryside, which inspired Thornton Wilder to write Our Town.
It is an area of relatively flat topography and productive farmland dominated by Mount Monadnock, which is placed prominently within the consciousness of the play’s characters. The trails range in difficulty from the relatively gentle ascent from the north to the classic Cliff Trail that requires scrambles up a number of exposed escarpments and traverses one bare sub-peak before joining the White Arrow trail that heads steeply up the south face of Monadnock.
The mountain also exhibits the characteristics of the glacially sculpted hills and mountains known as “roches moutonees.” This somewhat obscure geologic term (which translates as “sheepback rock”) refers to a massive rock outcrop with a gentle slope on the side from which the glaciers approached and a steep side in the direction in which the glaciers were advancing.
This “peak that became a paradigm” is a captivating sight at any time of year, whether cloaked in its summer greenery, capped with gleaming ice and snow, or decked out in glowing autumn colors. But whether one appreciates its grandeur from a car window or having ascended one of the challenging pathways to its summit, its splendid isolation makes it dominate the view for many miles around it in this quintessential New England landscape.
Chetro Ketl, a ruin at Chaco, shows a change that can be seen elsewhere in the canyon and in many other Anasazi sites: There is an imposing colonnaded wall of a building that resembles features found in Mayan buildings far to the south in Mexico and was perhaps inspired by them. But the spaces between the columns have been walled up.
If the name “Chaco Canyon” is unfamiliar or unknown to you, do not be surprised. I have found that very few people east of the Mississippi have heard of it. For that matter, I have run into very few people west of the Mississippi who know of it, even in the state of New Mexico in which it is located. (Of course, according to New Mexico Magazine, the number of people in this country who do not know that New Mexico is one of the 50 states is stunning — but we’ll let that go!)
Situated at the end of a bone-rattling 20-mile-long dirt road for which the expression “washboard surface” must have been coined, Chaco Canyon lies scores of miles west and north of Santa Fe, in a starkly beautiful stretch of desert. Blisteringly hot in the summer, achingly cold in the winter, it represents a section of high desert plateau incised many millions of years ago by a great river at a time when that part of the United States was far wetter than it is now.
Find Chaco on Google Earth and you will see that long-vanished river’s meandering course. Today the only water that runs through Chaco occurs when the heavy rains known as “monsoons” surge through the canyon in late summer, or when occasional winter snows melt. Then a muddy little stream known as Chaco Wash may flow briskly for a while, a pathetic reminder of the great river that millions of years ago cut its way down through the ancient rock strata of the plateau.
But there are many such canyons in New Mexico, Colorado, Arizona, and Utah. What makes Chaco important for more than its spectacular Martian scenery is the fact that a thousand years ago and before, it was the site of feverish building activity by the mysterious people long known as the Anasazi.
The term is Navajo and it is often translated as “ancient ancestors,” but it may also be rendered as “ancient enemy.” These days, in some quarters, the term has been dropped in favor of the more politically correct expression “ancestral Pueblo people,” but, as the evocative name “Anasazi” occurs frequently in the archeological literature, it seems appropriate to use it in this essay — which, after all, deals with the enigmas of Chaco Canyon.
The strata or “rock layers” of Chaco date from the Cretaceous Period of Earth’s history, and are roughly 80 million years old. They record a time when a vanished body of water known as the “Western Interior Seaway” covered this area.
It is a strange experience to hike the top of the plateaus surrounding Chaco Canyon and see fossils of corals, worm tubes, and shellfish in the rock layers that shimmer in the relentless heat of a New Mexican summer and to try to imagine the turquoise-blue sea that once covered the region.
And what would the ancient people have thought of them? The strata are composed of sandstone and shale — the latter sometimes mixed with poor-quality coal, forming black bands in the stark cliffs. Shales here as most everywhere are crumbly and brittle, but the sandstone is what geologists call “competent”: It is hard and makes excellent building stone. And here, starting in at least 800 A.D. and perhaps before, the mysterious Anasazi people settled and began to build.
Many United States travelers are familiar with Mesa Verde National Park in Colorado, where the Anasazi built their magnificent cliff dwellings. But there are many other such sites: Hovenweep, Canyon de Chelley, Navajo National Monument, and the Ute Tribal Park, to name just a few.
There, in the shallow shelters at the base of hard sandstone cliffs, these ancient people ingeniously constructed their stone villages, carefully fitting shards of rock together with the precision of the finest masons. The rocky overhangs offered protection from the fierce Southwestern sun as well as wind, snow, and rain.
But their lofty locations also offered protection from intruders — at least until some time around the year 1200 when something catastrophic happened. But more of this later.
What makes Chaco different from the other Anasazi dwelling places — and spectacular — is that here these people chose mainly to build sprawling free-standing buildings, some of them four stories high. In Chaco Canyon proper, there are at least a dozen such sites — and in the plateaus around it are many more.
Some of them are enormous, the largest being Pueblo Bonito, a great D-shaped structure featuring hundreds of rooms and dozens of kivas (round ceremonial pits). At its height, it may have been home to over one-thousand residents.
Adjacent to it and in various other areas of the canyon floor and the mesas above it, are many more such structures, varying in shape and size and building techniques, but all of them constructed from the billions of flat-rock fragments that weather from the cliffs and the surface bedrock, chinked with mud for mortar. They often form artful patterns, which in some cases may have been intended to mimic the patterns the Anasazi saw in the bedrock.
What is surprising is that the builders then apparently covered the walls with adobe, hiding their carefully crafted patterns. Perhaps they were motivated by the same impulse that drove the builders of Medieval cathedrals to insist on perfection even in those architectural details beyond the sight of worshippers on the grounds that they were intended for the eyes of the Almighty.
In any case, visitors to Chaco wander through the ruins in admiration of the sheer muscle power that must have been expended on their construction. Even in their ruined state, they inspire awe.
The making of myth
But it is the very vastness of the ruins that raises one of the questions that have troubled archeologists since the first Spanish explorers stumbled upon them in the mid-Seventeenth Century: For what purpose were these enormous buildings constructed?
The ruins in many of the other Anasazi sites were clearly occupied by extended family groups or tribes. In some of these sites, dried gourds and desiccated fragments of squash, beans, and corn may be found still in the places where the occupants left them —apparently having abandoned the structures on very short notice.
But vast areas of some of the pueblos at Chaco — in particular Pueblo Bonito — show few or no signs of habitation, having been meticulously constructed but apparently never occupied or even used for storage. And yet the ancient builders cleared an enormous network of roads stretching over 400 miles that radiate from Chaco, suggesting that this was meant to be an important hub of trade, religion, habitation — or perhaps all three.
And there have been additional discoveries that are disturbing. Beneath the dirt floors of some of the ground-story rooms, archeologists have found human bones that appear to have been systematically butchered, raising the frightening possibility of cannibalism, though some Native American Indians have insisted that these are more likely signs of rituals aimed at suspected witches. The issue is incendiary among modern pueblo people.
In addition, large quantities of jewelry and pottery have been found buried within the ruins, suggestive perhaps of attempts to hide them from invaders.
Curiously, in the Chaco region and in many other Anasazi sites, nothing remotely suggestive of a cemetery has been discovered — puzzling for a location that could potentially have had thousands of inhabitants.
Or could it? Given the fact that the land and climate a thousand years ago were not much different from those of today, farming would have been a daunting challenge; and, although the Anasazi were experts at what is known as “dry farming,” there are few areas of the floor of Chaco Canyon that show traces of the extensive cultivated fields of corn, beans, and squash that can be seen at Mesa Verde and other Anasazi sites.
There is some wild game — jack rabbits and some elk — but the sparse desert environment would hardly have allowed the existence of vast numbers of either animal.
So the questions remain: If the Chaco ruins were once occupied by great numbers of individuals, these people would have required enormous quantities of water; what was its source? How did the inhabitants raise or hunt enough food to survive? Where did they bury their dead? And what exactly drew people to Chaco from great distances along the broad roads?
One tantalizing hint comes from the so-called “Sun Dagger” site located on the magnificent outcrop known as Fajada Butte. Rising hundreds of feet from the floor of the canyon, the butte can be seen from over 20 miles away on clear days.
Though climbing it is prohibited to visitors, on its upper slopes archeologists have found three enormous slabs of rock carefully placed so that at each of the solstices and the equinoxes, sunlight moving through a slit in the rock is cast in various patterns on a spiral sun symbol, one of them knife-shaped.
Moreover, a number of the ancient pueblos have central features that seem to be aligned toward positions where the sun rises at various times of the year, evoking Stonehenge.
Combined with other things hinted at in Chaco, it raises the possibility that the canyon might have been occupied briefly for trade and religious rituals at specified times of the year and then stood largely empty for long periods.
But one looks at all of that has been written about Chaco Canyon and sees the words “suggestive of,” “possibility,” “perhaps,” “hints at,” “could have,” “might have” — and realizes that there is much that is unknown, and that may never be known, about this and other sites of the ancient pueblo people.
They did not have a written language, and all that is known about them has been passed down orally from one generation to the next by tribal elders. And, one-thousand years is a long time for historic events to become legend and then myth.
Mysteries of Chaco
Perhaps the most daunting question that arises when dealing with the Anasazi is why all of their meticulously constructed buildings were abandoned starting in the 1200s.
Tree rings record the onset of an extensive drought — but in addition to the fact that severe droughts are cyclical in the Southwest, this would hardly explain the apparent sudden abandonment of the ancient structures. All the signs indicate that at Chaco, Mesa Verde, Canyon de Chelley, and elsewhere, a time came in which the people simply grabbed whatever they could carry, damaged or destroyed what they could not take with them, and vanished into the deserts.
One particular ruin called Chetro Ketl at Chaco shows a change that can be seen elsewhere in the canyon and in many other Anasazi sites: There is an imposing colonnaded wall of a building that resembles features found in Mayan buildings far to the south in Mexico and was perhaps inspired by them. But the spaces between the columns have been walled up. And, as one explores the other ruins both on the canyon floor and on the mesas above it, one sees this process repeated: windows and doorways that have been subsequently filled with masonry.
Was this done simply for the purpose of strengthening the structures? Or combined with other unsettling facts about the ancient people, does it suggest an increasing need for security from attackers? Add these to the unanswered questions about Chaco.
Hike reveals more to ponder
One morning before the heat of midday came, along with a friend from Colorado, I set off to hike the plateau on the west side of the canyon. Carried on the dry morning wind were the combined smells of sage and juniper — what some have termed “desert incense.”
Our goal was the ruin called Tsin Kletsin, which lay at the end of a mile-and-a-half trail that led steeply at first up a series of switchbacks on some jagged cliffs and then over a much gentler slope dotted with Pinyon pines and juniper trees. The only animal life we observed consisted of some buzzards circling overhead — perhaps they were hoping we would be their next meal — and a rather emaciated-looking jack rabbit. We were glad we did not have to depend on wild game for meals.
For whatever reason, Chaco Canyon was nearly empty of visitors that day and we were the only hikers. The landscape below us was — as is most of Chaco — starkly beautiful, with tawny-colored cliffs, enormous piles of talus at their bases, and great embayments in the mesas, in which were nestled many of the ancient ruins.
But Tsin Kletsin was built at the high point of a dusty, windy stretch of desert, its fallen walls brooding darkly against the deep blue sky.
Like many of the other ruins, much of it is still unexcavated, with only a few of the remaining tiers of rock visible to give a sense of its general outline: rectangles and squares, covering thousands of square feet, and the inevitable circular kivas, all of them filled with shallow layers of dirt deposited over the centuries.
In places, small fragments of the Anasazi people’s distinctive black-on-white pottery lay amid the debris on the ground. The stone walls were surrounded by miles of parched landscape dotted with sage and cactuses and occasional junipers or Pinyon pines, some of them long dead and picturesquely twisted and blackened.
And it was there that another of the mysteries of Chaco struck us: Where did the builders get all of the stone to build Tsin Kletsin and some of the other ruins high on the mesas?
The pueblos on the canyon floor required enormous amounts of manpower, but at least the builders’ materials were lying everywhere at the base of the cliffs. But both Tsin Kletsin and a neighbor called Pueblo Alto on the distant north plateau lie a mile and a half from an easily available stone source.
What political or religious ideal could have driven the ancient workers to carry to this remote location the thousands of tons of stone required to raise these buildings? Yet another bewildering point to ponder.
Deep, dark skies
Chaco Canyon has always been known also as a place for lovers of the night sky, and, on Aug. 28, the International Dark Skies Association designated Chaco as the newest Dark Sky Park — a place where a viewer can get away from all artificial light and see the stars as our ancestors saw them.
The nights we camped in Chaco’s rather primitive campground we saw those fiery, cloud-flecked sunsets for which the West is celebrated, and we watched as the sky turned deep azure, then violet, and finally a black unblemished by the haze of cities or the humidity of other climates. Within it, the stars blazed brilliantly, showing shades of red and amber and blue.
The campground is situated close to Chaco Canyon’s north plateau, and at its foot are the ruins of two of the few actual cliff dwellings at Chaco. They are small, no more than fifteen feet square, and they are empty and dusty.
But their walls reflect the pale light of the stars and somehow in the night the tiny pueblos seem to be of this time and not ancient: Through their dark window holes, one expects to see the glow of a cook fire.
But it does not appear.
From the plateau above come the occasional howl of coyotes and the cool evening air is scented with sage and other desert plants; then the realization comes that one is experiencing the sights and the sounds and the smells of night just as the Anasazi did a thousand years ago.
And what had drawn them here? And where and why did they go? And what thoughts entered their minds when they looked up at the gleaming stars?
These and so many other questions frame the haunting mysteries of Chaco Canyon.
The Enterprise — Mike Nardacci
A textbook fault in a small limestone bluff in Joralemon Park shows two parallel layers of the rock known as “chert” within the limestone have been displaced by the fault’s movement. The layers on the left have been moved upward while those on the right have moved downward.
An old joke among people whose life interest is rocks is that, if you ask 10 geologists the reasons for an unexplained geologic phenomenon, you will get 10 different answers. Some of the answers will be stated with qualifications while some will be issued with Biblical certainty, and, as some of the explanations will be mutually exclusive, they may set off lively — even bitter — debates.
The wooded areas along Route 102 in Ravena — and in particular, Joralemon Park — have been known to geologists for decades as places of considerable geologic interest.
Among the area’s features are stretches of bare bedrock showing scratches from the passage of glaciers thousands of years ago; a series of easily visible faults produced by very ancient earthquakes; remnants of ancient caves; complex systems of active caves that have yet to be fully explored; sinkholes and karst ponds into which surface waters disappear or from which they emerge; isolated outcrops of 400-million-year-old Paleozoic bedrock, remainders of once-extensive layers deposited in pre-historic oceans; and massive boulders, some scattered randomly through the woods and offering no immediate clues to the reason for their presence.
Rocks, of course, do not simply appear out of nowhere. In mountainous areas, rocky sediments of all sizes weather and erode out of the exposed bedrock. In wide, flat areas far from mountains — such as large stretches of the Hudson Valley and much of the Northeast — rocks must be carried and deposited by streams or glaciers.
The rocks that turn up in farmers’ fields with the maddening frequency of weeds were deposited there thousands of years ago either directly by glacial ice or by the streams that poured from them when they began to melt.
In his great poem, “Mending Wall,” Robert Frost described such rocks found in the stone walls of New England: “And some are loaves and some so nearly balls/ We have to use a spell to make them balance:/ ‘Stay where you are until our backs are turned!’”
The important facts are that erosion by glaciers tends to take the sharp edge off of transported rocks while running water tends to make them more or less rounded; and that glacially deposited rocks are usually “erratics”: specimens of rock types that are not found locally and have often been brought from hundreds of miles away.
And so the Helderberg landscape is dotted with purple sandstone cobbles from Potsdam, rounded fragments of granite and anorthosite from New York’s High Peaks, and chunks of garnet-bearing metamorphic rock from the North Creek area. These sediments are referred to as “glacial drift” deposits and they cover much of the landscape of the Northeast.
And herein lie the puzzles of the Ravena rocks.
A mile or two north of the park, on Route 102, is a massive outcrop of rock that stands alone, looking to be more appropriate to some desert landscape of the Southwest than New York State. It is made of the 400-million-year-old Onondaga limestone, as is much of the surface rock of Joralemon Park, and local lore has it that Native American Indian artifacts were found long ago in the shelter on its north side.
Certainly, it would be an inviting place to spend a rainy night for a hunting party. Its layers lie horizontally on the surrounding terrain — it does not show the disturbance geologists call “displacement.” Moreover, its edges are rather jagged, not blunted; hence, it is unlikely to have been deposited there by a glacier.
While extensive excavation around it would be necessary to make a certain judgment, it is very likely an erosional remnant, a lone remainder of the thick layers of Onondaga limestone that millions of years ago covered the Joralemon area. There are other, smaller such outcrops scattered through the forest.
The massive outcrop is, in other words, likely to be “in place“ as geologists would say. The eponymously-named Joralemon Cave — its entrance yawns on the east side of Route 102 — is located in just such an erosional remnant, a segment of a long-vanished cave system.
The heavily-shaded interior of Joralemon Park contains numerous seeps and springs and swampy areas scattered beneath a forest of tall hardwood trees that trap much of the moisture. This creates an environment evocative of a rain forest, highly conducive to the growth of moisture-loving plants, which are remarkably diverse and prolific in the park.
A few hundred feet into the woods north of the bluff containing Joralemon Cave is an impressive high mound of giant boulders of Onondaga limestone. Its provenance is not so easily determined.
The boulders are wonderful to walk among in early spring and late fall — those times of the year when little growth is occurring, for they contain a collection of various types of mosses and ferns growing on and between them that would be damaged by foot traffic and that would delight any pteridologist or cryptogamic botanist (and yes- — I had to look up the terms!).
They are a spectacular place for children to play hide-and-seek or to imagine the boulders as the ramparts of a castle. Often 10 feet or more on a side, they contain between them innumerable overhangs and shady fractures and passageways, leading upwards or down, hiding places for toads and newts and the occasional black racer — a harmless but intimidating snake that in the Joralemon area can reach a length of six feet.
What is problematic about the boulders is that they are not horizontal to the surrounding bedrock. They are tilted or even upended as if piled there by a deranged giant.
Moreover, the tilts — what geologists call the “dip” of the rocks — are not uniform: One tilts north, its neighbor tilts south, and surrounding boulders may dip toward all the cardinal and ordinal directions on the compass.
Normally, in such a confusing display, a geologist would look on the rocks for “slickensides” — lines gouged into the bedrock when the two sides of a fault move, much as two cars scraping one another in opposite directions would scratch the surfaces. There are a number of such faults visible in exposed bedrock in Joralemon Park, evidence of one or more of the massive, earthquake-producing plate-tectonic events known as “orogenies” that have affected this part of the continent over the last 400 million years.
One of them is worthy of a geology textbook. But, as the boulders are covered in mosses, ferns, algae and liverworts, the slickensides — if they are there — are either obscured by the luxuriant plant growth or have been weathered away by it.
The point is that faults move massive amounts of bedrock during an earthquake. They may displace the rocks on one side of a fault upward relative to the opposite side or they may move them down; they may slide them sideways relative to each other or one side may dive under the other; and they are capable of distorting the rock structure in ways that have geologists scratching their heads trying to figure out just what Mother Nature was up to.
Amazing maze caves
A glance at a map of the active cave system in Joralemon Park may offer a clue.
Known as Hannacroix Maze (its waters feed the Hannacroix Creek), the cave is a true maze. If the prospect of getting lost within its labyrinth were not sufficient to intimidate explorers, the fact that it drains an adjacent beaver pond and is filled with fetid water inhabited by an assortment of creepy crawlers and swimmers usually does the trick.
Maze caves form in places where carbonate bedrock such as limestone or marble is heavily laced with the fractures known to geologists as “joints.” When waters containing mild natural acids — carbonic acid is common — enter the cave in times of flooding, the acidic solution is injected under pressure into every available crack and crevice, and voila! Chemical weathering forms a cave with a maze pattern.
One can easily notice, however, that between the cave passages are angular areas of bedrock. Should erosion eventually remove the roof of the cave, the result would be a rocky ramble such as the famous “Devil’s Den” in the Gettysburg Battlefield.
The “Devil’s Den” is made of igneous rock, not limestone, and the outcrops do not show displacement, so the situations are not exactly parallel. Still, both the cave and the battlefield outcrop represent bedrock in which erosion has occurred on the numerous joints the rock contains, resulting in a maze.
And so it would appear that the great rock pile in Joralemon Park must have resulted from the pre-historic movement of a series of faults running through a massive outcrop of limestone, eventually causing the weathered blocks to be left scattered helter-skelter in the forest.
Or so it would seem.
And yet — there are geologists who will defend the notion that the rocks are indeed glacially deposited — and that the reason that they consist of the same bedrock as the rest of the park and show little of the blunting that would result from glacial erosion is that they just have not been carried very far from their point of origin.
Perhaps it does not matter.
For the fact is that, within the wilds of Joralemon Park, lies a misty forest where water springs mysteriously from the bedrock; where marvelously diverse, unusual plants cover, it seems, every square inch of ground; and where Mother Nature shows her sleight-of-hand in strange geologic phenomena, through the agents of tectonics and weathering and erosion, over time beyond human comprehension.