Hand Lens - August 12, 2020

Issue №7: Drawn into the Basin

by W.L. Drawn to the Basin

Ascutney, right, at a distance of five miles; Little Ascutney, left, at a distance of one.

Remnant of a broad glacial lake draining from Quebec into the Long Island Sound, the Connecticut River stands only a few hundred feet above sea level as it flows along southeastern Vermont, sunk into the terraced plains of glacial clay that filled the depression left by a long-abandoned rift that once threatened to put an ocean between the already-ancient and worn-down fold-mountains of this part of New England. Ascutney, an intrusion of granite and syenite that ate into these mountains and now stands thousand of feet above them, eroding more slowly, is a lonely sight in the skyline of this part of the Connecticut--all the other plutonic mountains the rift allowed to puncture through stand further to the north and east. But Ascutney is not quite alone. Something like two million years before magma hardened in place there, it had already built a structure a few miles to the west. Today it has eroded into Ascutney Basin, an elevated piece of topography ringed by arced ridges, the tallest of which is only about a thousand feet above the Connecticut--Little Ascutney.

Viewed from the larger area, Little Ascutney looks only a little taller and a little steeper than the surrounding hills. From atop Ascutney, it looks curious only for its slightly-curved banana shape. It doesn't even enjoy the State Park status of its younger sibling-mountain, and is instead a Wildlife Management Area with unmared trails (I had to bushwhack to find the peak on my first visit) and an old farm field that receives a single annual mow to maintain a clearing ecosystem in the area. And yet, its peculiar geology and topography make it, in some respects, an even more fascinating locale.

By mid-June, Ascutney's towering waterfalls have all but run dry. The slow-weathering syenite of the mountain weathers slowly in part because a combination of composition and slope prevent all but the hardiest plants and lichens from finding purchase--in turn ensuring that the soil of the mountain is thin and cannot hold much moisture, even as the cloud-breaching peaks remain constantly damp. Composed of the same rock, Little Ascutney's ridges drain just as quickly--and directly into the basin, where, close to diorite bedrock, it tends to stay.

A string of wetlands dot the flattest parts of the area, each an acre or so of thick, spongy peat moss and slick-surfaced water slowly eating away at downed pine and birch. Here an abandoned beaver dam held back one of the deeper sections, full of green frogs singing as they sat and floated, largely still, under the noon sun. The croaks ranged in pitch from reedy calls you could hear from the rough trail passing a few hundred feet away down to profound basses that seemed to be sink into and reflect off of the moss in curious ways, making their vocalizers hard to locate--though perhaps I was distracted by the camera-fogging humidity raising off the water--or by the deer flies.

The streams leading down into the basin hosted easier-shoed mosquitoes flying above the water, and more curious creatures beneath.

Akin in nutritional niche, this beautifully-patterned leech might well threaten an unpleasant time for the half-dozen salamander larvae visible in this small portion of the stream.

Or perhaps not--as the blurriness of my photos communicates, these larvae were quick and aware. No matter how slowly or subtly I moved the macro lens I had submerged into the stream, in the time it took my camera to focus they were gone, inches down the stream and often well-hidden amongst the sand and rocks of the streambed. The sand here is primarily eroded from the gabbro, diorite, and syenite that build the basin and mountain--all of which, as speckled interleavings of small feldspar, mica, and quartz crystals, are uncommonly good matches to the patterning on these larvae. I would hazard to guess that these are Eastern Newt larvae, soon to emerge in red eft form--after eating great number of aquatic insects and other arthropods.

But perhaps this caddisfly would give them more than the usual challenge. The slender, white, long-legged larval form of the caddisfly eschews growing a tougher exoskeleton to survive the predation, instead building a sort of shell out of bits of detritus from the bottom glued together with its silk saliva. It keeps building this same shell as it grows, consistently adding material to the front in a widening radius. Curiously, all the individuals in a given pool or section of stream seem to construct their shells to the same pattern, quite distinct to other patterns in color, shape, length, and construction. How much is the product of the materials locally available, and how much is down to the specific lineage of caddisfly dominant in a given area?


"One afternoon in Mexico, the researchers attempted to recover eight Yaqui catfish caught in Cajón Bonito, which had escaped from some netting in a holding pond. This involved using a broken kayak paddle to maneuver a rowboat, which Minckley had purchased as a teenager to take duck hunting, out to the middle of the pond, and pulling up yards of soggy netting.
The men excitedly hauled a catfish to shore in a bucket and gently transferred it to a shallow rectangular container. The small, soot-gray animal burrowed into the corners, seeking an escape with its mouth and barbels. We crowded over it, and I found myself getting unexpectedly emotional, looking at what might be one of the last of an under-studied, barely known species, trying to escape from a plastic box. I felt foolish a few minutes later, when Varela-Romero checked its pit tag and announced that it was actually a Yaqui-channel hybrid. I wondered whether the loss of a species that looked just like one of the most common fish species on the planet really mattered.
Only later did it occur to me that perhaps, if I couldn’t tell the difference between a Yaqui catfish and a channel catfish, that was because they communicate in the language of fish, not primates — that their seeming interchangeability said more about my limited understanding than it did about their limited distinctions."

-- "The only catfish native to the Western U.S. is running out of water," -- Maya L. Kapoor.


This particular stream cut through a long-abandoned farm road--the properties that together form the core of the WMA were deeded to the state about seventy years ago, but had ceased to be productive farms well before that, with their wild apple trees only producing today as the result of Vermont's intervention. The road soon splits into a profusion of trails, one of which leads up to the rim of the largest of the ridges. It's not a long hike, but it is a steep one. The center of the basin was once a tall column of gabbro and diorite, but it too has eroded more quickly than the syenite and granites. Geologists who have studied the complex, like Jill Schniederman and Greg Walsh, suspect that this core of gabbro-diorite not only intruded first, but dissolved a great quantity of the surrounding rock into itself as it did so, leaving the final magma mixture more chemically vulnerable to erosion. The prominence of Little Ascutney today is mostly just the thin "ring dike" that formed around that column and filled in its cracks--as the gabbro-diorite magma cooled, it contracted, leaving space around the edges for new magma to intrude--magma rising up from the very same stock that formed the slow-eroding syenite of Mount Ascutney.

Exposed gabarro-diorite bedrock in the basin.

Syenite from Little Ascutney under lichen, exhibiting the same rusty-weathering as the syenite at Mount Ascutney.

However steep the hike from the basin to the rim is, though, it can't compare to the slope at the outer edge.

A favorite spot for rock climbers.

Along the rim, the surrounding metamorphic rock has fallen away to reveal the outer face of the ring dike--and to reveal, preserved in rock for a hundred million years, the impossible violence of the Ascutney Igneous Complex's formation.

Embedded in the rim are blocks, sometimes dozens of yards long, of phreatomagmatic breccia--instances where the rapid release of volcanic gases at incredible pressures utterly pulverized the rock surrounding the magma, re-binding it together into a sort of natural concrete (the meaning of "breccia" in Italian).

On older exposures, the breccia even looks like concrete--the differential weathering of all the intermingled chunks of metamorphic rock from all different strata, as well as the igneous cement, takes the look of fragmented old sidewalk left in a pile at the department of public works.

One can only imagine what must have been happening at the Jurassic surface as these massive acts of demolition occurred below.

These formations were only identified as phreatomagmatic breccia in the 20th century, but humans have been drawn to Little Ascutney by its geology just as surely as the frogs and leeches for far longer. A sort of oasis in an area that could grow quite dry into the depths of summer, farms and roads in the basin are mapped as far back as we have maps, and attested to by a network of gabbro-diorite stone walls--and, University of Vermont researchers suspect, have their origins in Abenaki routes through the area.

The high ridge of the dike draws people as well, the sheerest points in its rim devoid of trees and consequently offering unobstructed views out to the south--Hawks Mountain, the Black River, the North Springfield Reservoir.

What draws them? A cultural fascination with vistas? An evolved instinctual desire for the high ground? Some set of lineage-specific traits that converge on this point?

At one of the exposures, two cairns have been built out of breccia and rusty syenite, standing just a foot or so tall. The bottom stone of each of the cairns holds down a photo with its rough and angular edge, held tightly by a weight of a few dozen pounds. Both are five inches by three--standard--with one appearing to have been commercially developed from film, the other a reproduction of an older photograph. Both are portraits of an individual; both have been sun-bleached beyond recognition.




Little Ascutney from Stoughton Pond, five miles to the south.