Stories in Stone (15 page)

The zircons went haywire 2,680 million years ago.
Not only did the Morton rocks get folded like a gymnast, but they also got
an infusion of pink magma that finally, after nearly a billion years of boring gray, gave the rocks their distinctive coloring.
The fact that several nearby rock units record this same date means that an epic collision altered the Morton.
That collision
was between the block of rock that was the Morton’s home, known as the Minnesota River Valley terrane, and a much larger mass
of land, known as the Superior Province.

Mark Schmitz, a geologist at Boise State University who also studies the Morton, compared that impact to another impact that
occurred only 60 million years ago.
“Minnesota at 2.6 billion years ago would have looked like the modern Himalayas,” he said.
“There would have been a space problem as the two blocks came together.
They would start to deform and thicken.
As one block
slid under the other, pressure and temperature would rise and the rock would start to melt.” Or as another pair of geologists
wrote, the collision resulted in “manifestations of constipated subduction.”
²¹

Once again, partial melting would occur, with the tonalite spawning a melt but this time the melt was pink; pink magma that
injected itself into the gray tonalite as veins and pools.
Heat didn’t just melt rocks, it also weakened the Morton to a taffylike
consistency and caused it to swirl, surge, seethe, and eddy.
Most of the rock was still solid but the mountainous pile of
material above was squeezing and deforming the Morton like toothpaste and metamorphosing it into a gneiss.
Similar changes
may have occurred at the earlier events recorded by zircons but the continental collision 2,680 million years ago erased previous
textures and generated a metamorphic rock consisting of the bands of dark and light minerals that characterize gneiss.

The rock did not respond homogenously.
The basalt rafts acted plastically, and either bounced back to their original shape
or broke into fragments.
The pink granite and tonalite acted like Silly Putty, deforming but not breaking under pressure;
but the tonalite was less fluid than the pink granite.

One of the beautiful aspects of the Morton rocks is that you can see this give and take of rock.
In one panel pink dominates,
in another gray, and in a third, rafts of jet black basalt sit like islands awash in a sea of pink.
Some Morton building panels
look like still photographs of streams of blood flowing through arteries, a texture that quarry workers call veiny.
But the
dominant pattern resembles a series of pictures taken while stirring together cans of pink and gray paint.
Quarrymen call
this texture flurry.
²²

No matter which texture one sees in the Morton, the rock seems to be constantly in motion.
Nothing is static.
Although the
rock records events that took place between 3.5 and 2.6 billion years ago, it is the most alive rock I have ever seen.

The Morton Gneiss story, however, did not end with collision 2.6 billion years ago.
Two billion years ago, plate tectonic
action thrust the Morton up and for the first time in its multibillion-year existence, the pink and gray rock was at or very
near the surface of the planet.
After 2.4 billion years of action, the excitement ended.
Its story, though, was not over yet.
One more significant geologic event would have to hit the Morton in order for it to be exposed at the surface, but that landscape-altering
process would not occur until just thirteen thousand years ago.

Cold Spring Granite still owns and operates the Morton quarry, although they dismantled and scrapped their record-sized boom
derrick in 1996.
As happens with every product, fashion waxes and wanes and the Morton has been in a long-term wane; Cold
Spring quarries stone at Morton for only a few months of the year.
When I inquired about visiting the quarry, Dan Rea, vice
president for Cold Spring’s Commercial Division, was kind enough to open the site for me.

My guide was Mark Gross.
We reached the quarry by driving through a gate with a No Trespassing sign south of town, down a
dirt road, and parking next to an abandoned metal shed.
Like every other quarry I have seen, the multilevel, football-field-sized
stoneyard was strewn with massive blocks of cut stone and rubble piles of cut and broken stone.
It also had the requisite
scary-looking pit of cloudy water, which usually designates the oldest, now unused, portion of a quarry.
Rusty water streaks
stained the older cut walls, which towered fifty to sixty feet above the quarry’s main floor and provided good nesting locations
for swallows.
Other walls were dotted with hundreds of parallel grooves as if troupes of industrious clams had been in a synchronized
burrowing competition.
These holes had been drilled to break blocks off a quarry wall.

“We now only have a few men work the quarry and they are specialists,” said Gross.
Cold Spring removed their big derrick because
trucks and front-end loaders are more efficient.
Working a boom required at least four men—one to operate the hoist, one to
signal the operator, and two to attach the derrick cable to the block.
Operating the newer machines requires only one man
and is much less dangerous since multi-ton blocks no longer dangle from steel cables.

Gross called the process of quarrying “building a loaf.” Imagine a squared off quarry wall, flat on the top with two perpendicular,
vertical faces, one trending north, the other west, forming a corner.
First, a quarryman uses a hydraulic drilling machine,
which both pounds and spins a carbide-tipped drill, to cut a horizontal tunnel, up to eighty feet long, into the base of the
north face.
The three-inch-wide hole runs parallel to and eighteen feet from the base of the west face.
In step two, the driller
stands on the flat top and pierces the end of the horizontal hole with a vertical shaft as long as eighteen feet.
To cut the
rock, he threads a diamond-impregnated wire into the vertical shaft and down the horizontal tunnel and makes a loop by reconnecting
the wire’s two ends.
The loop feeds through a machine that moves the wire like a conveyor belt.
As the wire slowly cuts into
the rock, the machine tightens the loop and it slices through the rock.
This first cut of the loaf takes about fifty-eight
hours in the Morton rocks; cutting softer granite takes half the time.

The quarrymen have two options at this point.
They can either repeat the drilling and slicing process every six feet and fashion
slabs eighteen feet high by six feet wide by eighty feet long or they can make one shorter cut and create a loaf eighteen
feet high by eighteen feet wide by eighty feet long.
Since both the slabs and loaf are still attached at the base, the driller
drills a series of horizontal holes seven inches apart at ground level back to the eighty-foot-long horizontal hole he drilled.
He then pushes sticks of Dynashear, roughly equivalent in force to about one-twentieth of a stick of dynamite, back into the
holes, and detonates (or shoots) a slab or loaf, which pops free.

A buyer’s need and stone quality dictates whether the quarryman cuts a slab or a loaf.
Mausoleums may require wall-sized panels
of rock and use of a loaf, which the driller drills into slices, six feet thick by eighteen feet wide by eighteen feet tall.
In contrast, cladding or countertops use a long, skinny slab.
To work on the slab, drillers drive wedges into the long gap
made by the wire saw and force the slab to tip over onto old tires the size of a car or onto a pile of broken-up stone.
Smaller
blocks are made by drilling, which creates the burrowlike channels I saw on some walls of the quarry.

Unlike sedimentary rock, gneiss does not have to season or cure.
It can be worked immediately.
No further cutting, however,
occurs in Morton.
Blocks and slices get moved via a front-end loader onto trucks and transported to the Cold Spring Granite
factory, in Cold Spring, Minnesota, about ninety miles north.
Again, Dan Rea set up a tour for me.

After putting on a yellow hard hat and clear plastic goggles, I entered the cavernous fabrication, or milling, plant.
We started
at the gang shot saw, which looked like a bread slicer on steroids.
Instead of sharp blades, however, the machine used rows
of parallel steel plates that cut through the stone by moving back and forth, like a reciprocating saw.
The flat, quarter-inch-thick,
two-inch-tall steel plates, each about fifteen feet long, don’t actually cut the stone but grind a slurry of water and steel
shot—broken up bits of steel about half the size of a grain of rice—that do the cutting.
Operating twenty-four hours a day,
the incredibly noisy gang saw, named for its gang of blades, cuts through an eight-foot-thick block in three to four days.
It can cut panels as thin as an inch.

Cut panels, which moved through the building via bright yellow overhead cranes, next received a surface finish.
The first
finishing machine used pie-pan-sized, diamond-encrusted buffers and could produce a finish ranging from glassy smooth to coarse
and nonreflective.
For a rougher finish, Cold Spring had a machine that resembled a pizza oven and sounded like a jet.
Known
as a thermal finisher, its eighteen-hundred-degree Celsius torch expanded and exploded surficial feldspar crystals, leaving
a textured surface that works well for paving stones.
Cold Spring formed rough, natural-looking faces with a stone splitter,
which worked like a slow-motion guillotine to crack open a rock.
When the stone cracked it sounded like a gunshot.

Cutting took place on the other side of the building.
Computer-controlled, diamond-tipped circular saws cut most finished
panels.
Cold Spring had several with a variety of blades.
They use one of the blades mounted on a overhead arm to make round
columns by running the blade down the length of a column, rotating the column slightly, and moving the blade slightly out
or in and down.
Smoothing out the rough edges requires hand grinding and polishing.
Humans also perform some of the most high
precision work, such as cutting floral patterns into the rock.

For other intricate work, a high-pressure water jet can accurately cut to within one one-hundredth of an inch.
The water shoots
out at over nine hundred miles per hour at pressures of up to sixty thousand pounds per square inch (psi) and can cut stone
up to four inches thick.
By comparison, a typical fire hose operates at between one hundred and three hundred psi and a household
faucet at between sixty and eighty psi.

Cold Spring primarily sells the Morton Gneiss for buildings, monuments, tombstones, and mausoleums.
It is not popular, selling
about 8,000 cubic feet annually, compared with Cold Spring’s best sellers—a gray granite from Minnesota and a speckled, red-and-black
granite from South Dakota—both of which sell more than 120,000 cubic feet per year.
Despite the low sales for the Morton,
Cold Spring vice president Dan Rea was optimistic.
“Trends change.
There is always hope.”
²³

Twelve years after William Keating and Giacomo Beltrami ascended the Minnesota River,London-born George William Featherstonhaugh
(pronounced Fanshaw) traveled up the waterway in a birch-bark canoe that carried eight men and thirty-five hundred pounds
of supplies.
Known to the native people as the Stone Doctor and to the federal government as Geologist to the United States,
he reached the valley of the Minnay So-tor, as he spelled it, in September 1835.
Featherstonhaugh noted the unusual gneiss,
collected specimens, and made a perceptive observation: “It is evident that in ancient times .
.
.
the volume of the river
was many times greater than it is now.”
²⁴
He would be astounded by how much water once flowed down the Minnesota River valley.

This giant predecessor to the Minnesota River is called the River Warren.
²⁵
When it flooded thirteen thousand years ago, Warren shot down the valley and carried as much as 100,000 times more water
than what Featherstonhaugh encountered.
Fed by runoff from one of the greatest lakes to cover the planet—Lake Agassiz—Warren
spread across the entire valley, purging the land of soil and plants.
The turbulent water also stripped away cobbles, rocks,
and boulders deposited by previous glaciations, revealing the wonderful pink, gray, and black Morton Gneiss that lay below.

This final chapter of the Morton Gneiss’s 3.5-billion-year-long story began during the last ice age, when a tongue of the
Laurentide Ice Sheet retreated north back into Canada.
At its maximum the several-thousand-foot-thick glacier had covered
most of our northern neighbor and extended as far south as Iowa, but by 13,400 years ago, the climate had begun to warm and
the ice was disappearing.
Lake Agassiz formed along the southern boundary of the ice, at about modern-day Winnipeg.
It spread
mostly west to east, but one arm pushed south down into the United States along the modern-day Minnesota/North Dakota border.