October 9, 2020

GNEISS WORK:

The Stones of Lewis, Portals in Time (Hugh Raffles, 10/09/20, The New Yorker)

Lewis is a small place, but its story is immense. Four hundred and forty thousand years ago, ice, in places almost a half-mile thick, covered this land, turning the Outer Hebrides into something like northern Greenland today. The ice flowed east across the Minch to Scotland and back again; it flowed west into the ocean as far as St. Kilda, more than forty miles offshore. It transfigured the islands, scouring and splitting the bedrock, gouging out valleys and hills, advancing and retreating until the onset of warmer temperatures and heavy rains around 7000 BCE. The landscape it left was ragged and dramatic: roches moutonneĢes, whalebacks, crag-and-tail ridges, and frost-shattered pinnacles; giant erratics and smaller boulders dropped far from their origins; the desolate cnoc-and-lochan moors that trap the northern sun in countless pools like a splintered mirror.

As the ice ages melted away, the peat bog that now blankets much of Lewis began to grow. That peat, formed mostly from sphagnum moss and heather buried and compacted in acidic, waterlogged soils above the impermeable glacial till, was once the sole fuel for the island's crofters; and even today, it's cut and stacked to dry in dark, cairnlike piles. The peat here can be four thousand years old and deep enough to disguise or entirely cover ancient monuments. And below it, below the glacial till, is the bedrock, Lewisian gneiss, close to three billion years old, among the oldest rock on the planet, rock that started life as churning magma dozens of miles underground in the Earth's mantle, cooling, solidifying, and crystallizing into igneous granites, granodiorites, tonalites, basalts, and gabbros, then buried, reheated, sheared, and recrystallized, crushed, twisted, stretched, pressed, and folded in at least two major metamorphic, mountain-building events occurring over the next 1.5 billion years--warped and recast in such tortured ways that their original features, the defining traits of the protoliths of these islands, were thoroughly erased.

Lewisian gneiss, in the words of the archaeologist Colin Richards, is "rock that once seen and handled is never forgotten." Returning from Calanais one summer afternoon, I picked up two unassuming, hand-sized blocks on a jagged hillside littered with glacial debris as if from the aftermath of a planetary collision. As I write, they sit before me on the table: rough, coarse-grained granitic rocks, one with thick, confused layers of pale pink, the other larger, darker, "houndstooth stone" Seamus Heaney might have called it, implacable and exacting, he might have said, stippled black and gray matrix, thin parallel pink veins. One billion years ago, following millennia of uplift and erosion, the gneiss breached the surface with its psychedelic ripples and baroque bands--the gray and pink of quartz, feldspar, and granite; the dark green and black of hornblende and biotite mica. Resting on the sidelines in the Hebridean terrane, a foreland of the North American craton Laurentia on the margins of the long-closed, ancient Iapetus Ocean, it escaped the tectonic drama of the Caledonian orogeny, and so preserved the evidence of far older geological events.

The most solid of rocks, they're heavy; wary of dropping them, I hold them tight and think of them traveling through the frozen earth, the floating earth, the molten earth, the places they've been, the life they've seen, two-thirds of the way back to the beginning of the planet, far beyond the Ordovician with its horseshoe crabs, its cartilaginous fish, and its marine mass extinctions; far beyond the Cambrian with its trilobites, its brand-new chordates, and its paradigm-confounding explosion of multicellular organisms, the first eukaryotic cells, and the build-up of atmospheric oxygen; back beyond the Proterozoic and into the Archaean, the formation of the first bacteria and the first continental plates, an unsettled, still-cooling planet taking shape beneath an ammonia-and-methane-filled atmosphere; stopping just short of the lip of emptiness, the cusp of what geologists imagine as a liquid surface of swirling gas, brimstone, and fire, the hellish Hadean.

The A859 road to Calanais follows the stream of the Black River through northern Lewis, keeping close to what was probably the main land route to the monument in Neolithic times.

Approaching from the east, a succession of circles is silhouetted starkly against the sky on hilltops and outcroppings above the valley. Colin Richards and his team walked this and a second route to the principal monument at Calanais. It was as if they were moving through "a process of unwrapping," a theatrically structured and choreographed journey in which concealment progressively gives way to unveiling as the protected central space is neared. Richards and his colleagues decided that the sites they passed were something like movie flats, simulacra of monuments--circles flattened into ellipses to increase the visual impact from below, slabs selected for their prominent veins of reflective quartz and positioned to catch the sun, large stones propped up with blocks rather than mounted in sockets--quick, jerry-built structures in an architecture of deception and illusion.

By contrast, ever since the arrival of the writer Martin Martin in 1696, visitors have recognized that the central monument and its satellites were built to last. Martin, a native of nearby Skye, traveled to Lewis at the behest of the antiquarian, collector, and founding benefactor of the British Museum, Hans Sloane, then secretary of the Royal Society. A speaker of Gaelic, graduate of Edinburgh University, and tutor to chiefs of the Highland clans, Martin could move between two elites--the ideal envoy to a region that was as remote, primitive, and exotic to most Scots as it was to the London literati. Calanais, he reported, was "a place appointed for worship in the time of heathenism" where "the chief druid or priest stood near the big stone in the center, from whence he addressed himself to the people that surrounded him." Set high on its broad ridge, the site had an unusual cruciform layout. An imposing avenue leads to a small circle dominated by a giant monolith nearly fifteen feet tall; additional, shorter avenues reach out from either side, and, to the south, a single line of stones once stretched all the way to Cnoc an Tursa, a large outcrop of Lewisian gneiss, the rocky crag a hundred feet above sea level that I used to climb from Franki's house.

Posted by at October 9, 2020 6:16 PM

  

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