A couple of ‘Leave-its’: One in Albany County and the other in the Adirondacks

— Photo from National Park Service
Boxwork, at Wind Cave in South Dakota, is called cratework when it is this large.

A recurrent problem in geology is the sudden appearance of what researchers term a “leave-it.”

Surrounded by his grad students, a professor has examined a site; rock outcrops and sediments, and erosional or tectonic phenomena have been observed, and, following appropriate consideration of all of the facts, the professor proposes a theory to explain the site. 

Then someone — one of his grad students, or worse, someone with no geologic training whatsoever who just happens to be accompanying the researchers on their field excursion — picks up a rock, shows it to the professor, and says, “What’s this?”

It happens that “this” is the proverbial monkey-wrench in the works, the very presence of which undercuts the entire carefully-constructed theory of the site’s origin and history. After careful examination, the professor may toss the sample in hand once or twice and then give it a mighty heave, while mouthing the words — “Leave it!”

While there are undoubtedly more “leave-its” in New York State than many scientists would want to admit — and they are by no means confined to the geologic sciences — there are two in particular, one in Albany County and the other in the Adirondacks, worthy of consideration.

Interesting mysteries in themselves, they are also reminders of the fact that nature has many secrets, and human abilities to decipher them in the end are not without limits and should inspire humility in all science researchers.


The “Boxwork” rocks of the Clarksville Gorge

On the edge of the village of Clarksville is a gorge through which flows the Onesquethaw Creek. Cut millennia ago when the great glaciers were melting and the Onesquethaw was vastly more voluminous and powerful than it is today, the gorge features small caves and springs in rugged limestone cliffs towering over terraces pockmarked with potholes along with mounds of sediment carried down by the Onesquethaw from bedrock layers higher in elevation in the Helderbergs.

There are also pebbles and cobbles scraped from the bedrock and transported from the Adirondacks and regions above the Canadian border and then left in great deposits of sediments as the glaciers retreated. Such rocks are called “glacial erratics” and identifying their sources allows geologists to map the paths of advancing glaciers. The gorge is a veritable textbook of geologic processes.

Yet, among the chaos of sediments, a patient observer can find some curious rocks that are wildly out of place in this part of New York State and whose ultimate bedrock source is a mystery. The rusty-red sandstone rocks are found as jagged samples, their color revealing the presence of quantities of iron — the same element responsible for the color of the landscapes of Utah and the planet Mars.

But what makes the samples unusual is the fact that they are highly fractured, and the intersecting fractures are filled sheets of white quartz, formed from the silica that makes up much of the sandstone matrix and forced into the fractures under immense pressure.  Known to geologists as “boxwork,” structures such as this are sometimes found in caves such as Jewel Cave and Wind Cave in South Dakota.

But these caves are dissolved out of limestone — made largely from calcium carbonate — and the sheets that make up the boxwork are pure calcite, which is more resistant to weathering and erosion than the limestone and the “boxes” therefore tend to project from surfaces.

And the question arises: Where did these rocks come from? There are no rock layers in Albany County or the lands to the north in New York State whose bedrock is known to contain structures such as the boxwork in these samples.

Glacially-transported rocks are usually somewhat rounded off, their sharp corners abraded by slow grinding against other hard sediments within the ice.  Some of these rocks are partially rounded but many are jagged — though the presence of the angular “boxes” would likely result in fracturing rather than rounding.

And then there is the question of why these rocks are found in the Clarksville gorge of the Onesquethaw but are not reported from other sites in the Helderberg area or elsewhere in the state. “Leave-its” indeed!


The “Tafoni” of Snowy Mountain

Above Indian Lake in the Adirondacks looms Snowy Mountain. Rising to 3 898 feet above sea level, Snowy falls 102 feet short of being a true New York State “high peak.”

But it offers sweeping views of the surrounding mountains and lakes and its location west of many of the other soaring summits crowned by Mount Marcy make it less likely to be the goal of “peak baggers,” especially on weekdays. Snowy’s bedrock is a mélange of the rock types shared by most of the mountains of the Adirondack region: igneous and metamorphic rocks such as granite, gneiss, schist, gabbro, and anorthosite.

On a slope of Snowy Mountain and not far from a meandering highway is a collection of enormous boulders known as “tafoni.” The term is obscure; my dictionary of geologic terms published by the American Geological Institute does not even list it. According to Wikipedia, the word may be of Sicilian or Corsican origin and simply means “rocks with holes.”

On the other hand, the similar phenomenon known as “honeycomb weathering” is well known to geologists and found fairly commonly in the states of the “Four Corners” area in the Southwest. I recently photographed a textbook example along the highway known as the “Turquoise Trail” that runs southeast from Santa Fe, New Mexico.

Honeycomb weathering generally occurs in rock that contains or consists mainly of calcium carbonate — limestone and calcareous sandstone — and forms when the slight acidity of rainwater chemically dissolves the mineral randomly over centuries, producing the pockmarks.

Some igneous or metamorphic rocks also contain calcium carbonate or other minerals that may dissolve very slowly in natural acids but it is believed that sandblasting can also create honeycomb weathering. A combination of chemical weathering and sandblasting may well explain the tafoni of the Turquoise Trail outcrop and that of other sites in the Four Corners states.

New York’s tafoni lie in a heavily-wooded area on a fairly steep section of Snowy Mountain’s western slope: enormous boulders covered in mosses and fern gardens, pocked with pits of varying depth, some only a couple of inches in diameter, others big enough to walk into.

The larger hollows frequently have smaller pocks within them. Chalk markings and abrasions show that some of the largest have been climbed by boulderers and one has a rickety old ladder, allowing a precarious ascent to its top.

But the enormous tafoni of Snowy Mountain present a puzzling case. For one thing, the boulders do not contain calcium carbonate or any other mineral that dissolves readily, even when doused in hydrochloric acid.

They also are clearly not “in situ” — in other words, they are not weathered remnants of the slope on which they are located. They are somewhat rounded and they are not attached to the ground, clearly having been transported there either by tumbling from a higher location on the mountain or dumped there by glacial action.

But none of the cliffs and other exposures of the bedrock of Snowy Mountain show honeycomb weathering and there are no expanses of bedrock north of the mountain in the Adirondacks that are known to yield boulders that have weathered into tafoni.

Moreover, they are surrounded by thick forest, which would seem to preclude sandblasting as the cause of the pits, although in millennia past, in the wake of the glaciers, the slope would have been barren of protecting forest cover. In any case, the question arises — as with the boxwork rocks of the Clarksville gorge — where did the tafoni come from and how did the pits form?

Perhaps the solutions lie in the future in the research of graduate students completing theses for degrees.

In the film “Jurassic Park,” a biologist, contemplating the ingenuity of the dinosaurs, utters the famous line, “Life will find a way.”

And Earth’s restless crust and the great forces that churn beneath it also frequently confound science. Two-hundred years ago, most scientists and scholars believed that our planet was 6,000 years old and that all the great changes that had shaped its surface were divinely directed. 

A hundred years ago, before the theory of plate tectonics was backed with irrefutable evidence and accepted as the cornerstone of modern geology, Alfred Wegener was almost universally derided for the notion that the Earth’s continents and seafloors moved around its surface like giant rafts.

And, among many other mysteries in modern science, geologists and biologists alike are intrigued by the source of the methane being detected emanating from the surfaces of Mars and Saturn’s moon Enceladus.

Mother Nature clearly does not play by our established “rules” and has many more mysteries — and surprises — in store for us yet.