The lost stone quarries of the Helderbergs once paved city sidewalks and grand buildings

— Photo by Mike Nardacci

A polished slab of Becraft limestone shows its numerous Devonian period fossils.

— Photo by Mike Nardacci

The Knox Fossil Rock Quarry is now inactive.  The subject is standing on an outcrop of Becraft limestone right at its contact with the overlying Oriskany sandstone.

— Photo by Mike Nardacci

A dilapidated lime kiln in Joralemon Park near Ravena is one of dozens scattered throughout the Helderberg region

— Photo by Mike Nardacci

The stone wall in the historic cemetery on Peasley Road near Rensselaerville is constructed of Helderberg bluestone.

— Photo by Mike Nardacci

The abandoned Helderberg bluestone quarry in the formerly bustling village of Reidsville is quiet now.

— Photo by Mike Nardacci

The Rock Hill Road limestone quarry, the products of which were once used in the manufacture of Portland cement, has long since been abandoned.

— Photo by Mike Nardacci

An exterior wall of the Western Diner in Guilderland shows numerous brachiopod fossils found in the Oriskany sandstone.

With the Helderberg landscape buried under yet another huge snowstorm in this seemingly endless winter, many of the unique geological features of our area are hidden beneath the drifts.  Fortunately, the subject of this column is fine for the “armchair” geologist — all that is needed being a good imagination!

I put together a number of photos I took with the help of my reliable assistant, Devin Delevan, in the fall and during that warm period we had in mid-December — and voila! — a meditation on the ancient rocks of the Helderberg Plateau and the long-abandoned quarries from which they once were drawn.

And I would like to start with a site which is one of the most accessible — at least when the region is not groaning under the weight of all this snow.


The hamlet of Reidsville is today but a shadow of what it once was.  “Blink and you will miss it” is an apt cliché.  It lies on the Cass Hill Road, a lovely stretch of back road that climbs steeply up onto the hills above Clarksville and passes through miles of forest filled with rambling old stone walls before intersecting with Route 85 just west of Reidsville.

The hamlet consists of a few houses, a barn or two, and a mossy old cemetery whose occupants surely outnumber the current living population.  But back in the first third of the 20th Century, Reidsville was a bustling town of hundreds of inhabitants and featured two churches, a number of stores — and the bustling Reidsville bluestone quarry. 

The quarry today is unimpressive and easy to miss.  A broad depression lying on the north side of Cass Hill Road as one approaches the hamlet’s crossroads, it is filled with stagnant water and cattails, a haven for peepers in spring and bullfrogs in summer.

A couple of abandoned tires have been dumped into it.  Other vegetation has taken hold in the dry areas and only the angular outcrops and low vertical cliffs hint that the depression is not natural.

In the wooded areas surrounding it, piles of the shattered bluestone once quarried there lie covered with weeds and the debris of eight decades of seasonal changes.  According to a 1934 article in The Enterprise, the quarry ceased operations in 1933 due to the arrival on the scene of a building material that, although used extensively by the ancient Romans, had recently become easily-available and relatively inexpensive: concrete.

And, in fact, Portland concrete doomed hundreds of other stone quarries throughout the Northeast and elsewhere in the United States as cut stone — once essential for many building projects — became prohibitively expensive and began to be used more commonly as a luxurious decorative facing stone.  (An old geologists’ joke says that the difference between “rock” and “stone” is that stone is rock you have to pay for!)

And, indeed, looking around the older parts of cities, one notices far more cut stone than would be found in most modern-day building projects.  The massive amounts of white Vermont marble facing the buildings of the Empire State Plaza contributed to the enormous cost of the project.

A television documentary recently revealed that, for a while in the early 1960s, New York State wanted the Albany Catholic diocese to encase the venerable Cathedral of the Immaculate Conception — built from red sandstone — in the same white marble as the plaza so it would “blend in.”  Obviously, the cost of such extravagance was a major factor that contributed to the shelving of that idea — and, one would hope, someone’s sense of historicity and aesthetics did as well.

A 1935 geologic map of the Berne Quadrangle shows that the Reidsville quarry was one of numerous bluestone quarries once active in the Helderbergs, and a drive around some of the back roads of the area will reveal them to be in a state similar to the one at Reidsville.  But for many years they provided work for hundreds of laborers, and their products are visible in areas such as downtown Albany and Troy where sidewalks were frequently constructed from the stone.

Helderberg “bluestone”

In this part of New York State, “bluestone” is a common term for a hard sandstone of late Devonian age — roughly 360 million years old.  It is not really blue — in its freshly-cut stage, it is a rich, attractive dark shade of gray sometimes tinged with green and it tends to weather to black or brown depending on its iron content.

Helderberg bluestone originated in what is known as the Catskill Delta that emerged during the Acadian Orogeny (mountain-forming episode) as the landmass that would one day be called Europe collided with proto-North America and threw up a series of lofty mountains to our northeast.  The sediments that washed down from those mountains filled in the shallow tropical sea in which our local limestone layers formed and produced a series of interlocking deltas, creating environments in which forests of some of the earliest large land plants would emerge.  The Gilboa Petrified Forest is a well-known example.

In the Helderberg area, the rock does not typically show many fossils, though in other locations it may feature trilobites and brachiopods and other typical Devonian marine fauna, most of which are extinct today.  In Oneonta and the upper Catskills, the fern tree fossils and fragments of some of the other early land plants become common, evidence that the strata in which they occur formed in non-marine environments.  

Today, much of the bluestone that is still quarried commercially is sold from outlets such as the eponymous Helderberg Bluestone on Route 443, which takes the stone from but a single active quarry.  Since it easily separates or is cut into flat slabs, it is used widely in retaining walls, just as it has been used for hundreds of years in the Helderbergs for walls and foundations.

The historic cemetery on Peasley Road near Rensselearville features a beautifully constructed example.

Oriskany sandstone

Another somewhat less commonly used Helderberg building stone is known as the Oriskany sandstone, named for what geologists call its “type location” at Oriskany Falls in Oneida County.

The Oriskany is what is known as a “calcareous” sandstone, meaning that it has a high content of calcium carbonate in addition to quartz sand and it is believed to represent both near-shore and on-shore ancient beach deposits. Such beaches are found in many tropical areas of the world today and Acadia National Park’s famed “Sand Beach” is a temperate-zone example of the type.  

It is a relatively thin layer — averaging no more than 2 to 4 feet in most areas of the Helderbergs though it thickens greatly to the south of the area.  The Oriskany is widely prized as a decorative facing stone because it contains enormous quantities of large brachiopod fossils, which stand out impressively as the rock weathers.

A currently inactive quarry near the village of Knox on Route 156 — formerly known as the “Knox Fossil Rock Quarry” — was used for years as a source of the Oriskany.

A wonderful display of its fossils may be seen in the fireplace of the old Hofbrau Restaurant on Warner’s Lake (now the Maple Inn) and exterior walls of the Western Diner on Route 20 in Guilderland where the large — sometimes fist-sized — shells of the ancient creatures appear in the thousands, some in fragments but many intact, just as they would have been found on a Devonian-Period beach.

When the Oriskany is exposed to years of weathering, the carbonate materials tend to dissolve away, often leaving the sea shells — with a high silicate content — easily visible.

Limestone layers

The Helderberg escarpment that rises to the west of Albany is composed of three major limestone layers.  The thin-bedded Manlius limestone and the massive Coeymans limestone above it make up the more prominent cliffs, visible from many miles away on a clear day as a stark gray band, tilting gently to the south. The two are believed to have formed from the carbonate-rich ooze at the bottom of a relatively warm, shallow sea during the Devonian Period. 

Many Helderberg and Schoharie area caves are formed in these limestone units, which dissolve readily in naturally occurring acids.  In the stretch of countryside between Altamont and New Salem, the two layers have a combined thickness approaching one hundred feet, maintaining a similar thickness as they stretch south along the Vly Creek Reservoir

Approximately 140 vertical feet higher is a second, slightly less prominent line of cliffs composed of the Onondaga limestone, also a major former of caves. The Onondaga is light gray and in its lower reaches contains layers and nodules of chert, a hard silicate rock commonly known as flint.

Above Thacher Park, the upper Onondaga forms an extensive flat landscape known as a “bench” on which the northern stretch of the Beaverdam Road was constructed, and along which numerous small sinkholes and some short caves have formed.

None of these three limestone units has been widely sold as a commercial building stone, but the relative purity of all three layers made them valuable in the making of Portland cement in years past.  The limestone was harvested from now-abandoned quarries such as the one found on Rock Hill Road near the Vly Creek Reservoir and smashed into jagged boulders, which were then burned in wood-fired lime kilns to drive off the volatiles.

Ruins of many of these kilns lie scattered throughout the Helderbergs, often covered with mosses and lichens and calling to mind the so-called “Beehive” buildings constructed by the ancient Celts and scattered throughout western parts of the British Isles and France.  Locally, Callanan Industries and the extensive quarry in the village of Howes Cave continue to quarry limestone for this purpose.

All three of the units also found use in the construction of foundations for houses and sometimes entire buildings, as testified to by the beautiful stone dwellings in the Onesquethaw Valley south of Clarksville and the handsome Onesquethaw Reformed Church, all of which were built from the Onondaga.

And, of course, the hundreds of miles of old stone fences that lace the woods of the Helderberg and Cobleskill plateaus were built of these and other types of rock found locally and constitute some of the best places to collect Devonian period fossils.

The last and perhaps rarest of the Helderberg area stone used decoratively is the beautiful Becraft limestone.  The Becraft is not widely exposed on the plateau, and in most places it has a thickness of only 12 or 13 feet, though, according to the well-known New York State geologist Winifred Golding, in its type locality — Becraft Mountain near Hudson — it reaches a thickness of 45 feet and was also once quarried in the making of Portland cement.

It is described as an example of “coquina,” made up almost entirely of variously-sized shell fragments cemented together — in this case by calcite.  Coquina tends to form in what are called “high energy” environments: areas in which powerful waves remove very small fragments but leave behind enormous quantities of whole or partial medium-sized shells that then get naturally cemented together.

The Becraft is thus a very hard rock and, when broken, it tends to have a great many jagged edges — the protruding shell fragments.  The only quarry I am aware of in the Helderberg area where the Becraft was cut commercially is again the old Knox Fossil Rock Quarry.

Due to its hardness, the stone will take a high polish and was used for decorative counters and tabletops.  An example is on an antique dresser that I refinished a number of years ago and for which I purchased a polished slab from Helderberg Bluestone to replace its damaged top.

Strata with evocative names

There are a number of strata of other rock-types found in the Helderbergs which have evocative names but have found less commercial use:  the New Scotland limestone, the Brayman shale, the Rondout waterlime, the Esopus grit.

These strata, along with those discussed above, form a gigantic layer cake, some of which is visible in natural outcrops, much of which is buried under layers of glacial sediment and luxuriant forest growth.  To the geologist, the strata indicate episodes of ancient seas rising and falling, of continents colliding, of ecosystems changing, of strange creatures evolving and flourishing or going extinct.

And, for the inhabitants of the Helderberg area, they have long provided stone for purely practical purposes, of course, but they have also provided materials for decoration that are not only beautiful but tell of diverse worlds, gone forever into the labyrinths of the ages.