Stories in Stone (18 page)

At the quarry on Anastasia Island, the first task was to clear away the scrub oak, palmetto, and rattlesnakes and reach the
coquina, which lay under a thin layer of soil.
Peons used axes and picks to cut grooves deep into the soft stone.
They pried
out blocks with wedges and pry bars, taking advantage of layers of sand within the coquina that formed a natural splitting
surface.
A waterlogged block, two feet thick by four feet long, required six men to lift it.
Workers transported the blocks
by cart to a creek, where they loaded the stone on boards laid across the canoes.
On the far shore north of the fort, more
men unloaded the blocks, which needed to season for at least a year.

Workers also proceeded with lime production essential to making mortar.
By March 1672 the kilns had generated sixty-three
hundred bushels of burned-down oyster shells.
They had most likely been collected from shell middens that dotted the coast.
Native people, who had inhabited coastal Florida for thousands of years, relied heavily on oysters in their diet and had generated
the shell mounds, which could stretch for several hundred yards in all directions and rise tens of feet.

Engineer Daza finally arrived from Cuba in midsummer.
Governor Cendoya, Daza, and other dignitaries broke ground for the foundation
trench at four P.M.
on October 2, and on November 9 they laid the first block of coquina.
Everything was ready for quick construction
of the castillo made of clamshells.

Coquina around St.
Augustine is like George Washington on the East Coast: everyone wants to claim a connection.
You can live
in a planned community at Coquina Crossing, bowl at Coquina Lanes, and pray at Coquina Community Church (based on a “more
reliable foundation stone, that of Jesus Christ”).
You can buy bags of coquina, too.
The city visitor center offers a better
deal than the national park.
For $2.83 you get two marble-sized bits and a confusing fact sheet that calls coquina both a
“natural limestone” and a “rocklike substance.”

You can also visit three sites on Anastasia Island with signs stating that stone for the castillo came from that particular
location.
A coquina chimney and an old coquina well filled with trash stands near one sign.
Nothing nearby looks like a quarry.
Another sign stands near a swimming-pool-sized pond, a good spot to see great blue heron stalking small fish.
¹⁸
Again, no surface feature indicates that this might be a quarry.
The third seems the most likely, with low slopes of coquina
rising from a one-hundred-yard-long, fifteen-yard-wide shallow depression.
It is also the best-marketed site, with prominent
signs and two brochures describing its history.

Considering the size of the castillo—Joe Brehm said that a geologist estimated that over five billion pounds of stone had
been used to build it—each of the signs is probably correct.
What may be more surprising is that more sites don’t make the
same claim.

Site number three is on the northwest edge of Anastasia State Park, on the east shore of the island.
A carved wood placard
nailed to a slatted fence designates the area as “Old Spanish Coquina Quarry.” Behind the sign runs a flat, shell-fragment-covered
path, which curves through two hundred feet of scrub oak and palmetto into a clearing.
If you arrive early in the morning,
the sun may backlight mist rising from warmed grasses and low shrubs growing in the quarry bottom.

About sixty feet from the opening, a slope of tan to white shells and shell fragments weathers out of a ledge of coquina.
Tucked into an overhang of ferns and shrubs, the top layers of fresh coquina are peachy to orangish tan, a result of oxidation
of iron in the stone.
Most of the wall is the more typical tan, which subsequently bleaches out in the sun to the gray of
the castillo.

The drab colors of coquina, the stone, fail to convey the beauty of coquina, the clam.
As the specific name,
variablis
, implies, no two look alike.
Never uniform and always complex, the colors can be banded, like growth rings, fingered, like
rays of sunlight, or both.
Set against a yellow, ivory, or white background, rays and bands can be yellow to russet, blue
to purple, pink, gray, or any mixture of these shades.
Such variation has led to common names of butterfly shell and periwinkle.

The
Donax
’s kaleidoscope of pattern and color helps make the clams less visible to predators, such as oystercatchers, sanderlings,
and ghost crabs.
One way to locate coquina clams is to look for groups of birds probing the sand to find the buried bivalves.
Less mobile predators include moon snails, which nab
Donax
with a lightning dart of their foot, and lettered olive snails, which latch onto a coquina and pull it under the sand for
a subsurface snack.
Fish also eat coquinas or at least have the “nasty habit of biting off the siphons,” says marine biologist
Olaf Ellers.
¹⁹
Coquinas have two siphons: one for sucking in food, the other for expelling waste.

People also eat coquina clams.
The earliest evidence of people inhabiting what is now Florida comes from coquina shell middens
fifty-seven hundred years old.
Ancient beach dwellers appear to have eaten coquina clams seasonally for thousands of years.
Archaeologists don’t know exactly how prehistoric people ate coquinas, but modern molluskivores prefer a broth, which writer
Marjorie Kinnan Rawlings describes as delicate and delicious.
²⁰
She recommends serving it piping hot with “two tablespoons thin cream and a small lump of butter.”

At the quarry, away from the prying eyes of law-abiding, law-enforcing national park rangers, you can run your hand over the
coquina.
Shells will spill out and cascade down the slope.
In some layers, roots poke out, having penetrated over a foot deep.
They look as if they would slice through the rock if you pulled on them.
How could anyone think this clammy material would
be good for building, particularly for a fort to protect a town from rampaging pirates and overzealous Englishmen?

Known officially as the Anastasia Formation, the 110,000-year-old layers of coquina outcrop as a wisp along the east coast
of Florida from Anastasia Island south to Boca Raton.
Stretching for 225 miles, the rock formation is never wider than 10
miles and seldom thicker than six feet, although some beds are up to fifty feet thick.
²¹
Made primarily of shells, shell fragments, and quartz sand, the Anastasia can be seen at Marineland, Flagler Beach, Blowing
Rocks Preserve, and House of Refuge (in Martin County).

Close-up of coquina showing shells.

Coquina is geology in its most elemental form: not quite rock and not just a pile of shells, more a stone during its gestation.
It is sort of the geologic opposite of Morton Gneiss.
Every species found in the Anastasia can still be found living on beaches
in Florida.
No life existed on Earth when the gneiss formed.
In the gneiss you can see how billions of years of geologic processes
have melted, mixed, and metamorphosed the rock, whereas the coquina doesn’t appear that different from the day it first formed.
Look at gneiss and you can tell it is very hard rock.
Touch coquina and you can feel that it is very soft rock.
Part of the
appeal of coquina, at least to a modern visitor, is its elemental simplicity.
You can easily understand how a stone forms.

Imagine a beach, any beach where clams and cockles and scallops and crabs live.
They die.
In places, the currents sort the
remains into homogenous piles of small clamshells.
In other locales water mixes the shells into heterogeneous heaps.
Time
passes.
Rainwater washes down into the piles and dissolves away the calcium carbonate that makes up the shells.
Gravity pulls
the water down into the pile.
The water becomes saturated and begins to deposit minute crystals of calcium carbonate on any
surface the water touches.
The crystals cement the shells together and coquina is born.

The new coquina changes little for hundreds of thousands of years, but if we peer into the future, we would eventually see
new materials, such as sand, silt, and even more shells, beginning to accumulate on the coquina.
The weight would compress
the layers, which would become denser.
More cement would accumulate and after millions of years, the coquina would now look
like a rock, solid and hard.
You would still recognize the fossils but no original calcium carbonate would remain.
The coquina
would now be a true limestone.

In the Anastasia, cementation, or lithification, was aided by the
Donax
shells.
Like most bivalves,
Donax
shells are made from calcium carbonate, but not the usual form of calcium carbonate, called calcite.
Instead,
Donax
are made from aragonite, a less stable form of calcium carbonate.
If
Donax
had been made from calcite, rainwater would not have been able to dissolve the calcium carbonate as quickly, and the shells
may not have been cemented together into coquina.
The Spanish might not have retained Florida and life as we know it may have
been completely altered.
Fortunately the clam was there.

Donax
clams also affect coquina after the stone has been quarried.
In contrast to how brownstone seasons—by internal water transporting
minerals to the stone’s exterior where calcite and silica reprecipitate on the surface—coquina hardens through external water,
either rain or runoff, dissolving aragonite and precipitating cement near the surface.
In both cases, seasoning creates a
harder shell, sort of like chocolate coating on an ice cream bar.
²²

Lithification occurred and still occurs very rapidly in the Anastasia Formation.
South around Cape Canaveral, perfectly preserved
ghost crabs, which died in their burrows, have been frozen into the coquina.
They look like some twisted version of Shake
’N Bake with grains of sand, shell bits, and calcite coating the crab carapace.
²³
Closer to St.
Augustine, lithification has locked Coke bottles in place.

Deposition of the Anastasia occurred in a high-energy, shallow marine environment.
Specifically, the coquina accumulated in
the swash zone, the area along a beach intermittently covered and uncovered by waves.
If you think about any swash zone you
have seen, you will realize that it is a harsh environment, with waves constantly pounding and abrading the beach, which helps
explain the abundance of shell fragments.
And because of currents and storms depositing sediments, layers of nearly pure sand
periodically interrupt the layers of shells, which created the zones of weakness that quarry workers exploited in order to
split the coquina into blocks.

The swash zone is an ideal habitat for coquina clams, says Olaf Ellers, who wrote his Ph.D.
dissertation on the mollusk’s
migratory movements.
Winter finds
Donax
offshore in deeper and safer water, away from predators.
During warmer months, they follow daily tides, moving inland with
a rising sea and seaward as the water retreats.
Their goal is to situate themselves in the swash zone where moving water suspends
food particles.
Once they reach their ideal location they use their shovel-like foot to dig themselves into the sand.
Bad
weather doesn’t stop coquinas from their travels, as Ellers found out when he snuck into a hurricane zone while working on
his dissertation and watched coquina battle the big waves.
I don’t recommend following Ellers’s lead.

To facilitate movement, coquinas pump their foot up and down like a pogo stick to leap into the surf.
Ellers coined the term
“swash-riding” to describe this molluscan leaping and surfing.
Like their human counterparts, coquinas are picky about their
waves.
“They choose only the 20 percent of waves that would carry them the furthest distance shoreward,” he says.