Tuesday, April 28, 2009

Plants and Stone: Castillo de San Marcos

I wanted to follow up my previous posting on plants and geology and turn a little closer to home, though this posting features a building more than 3,000 miles from my home. In St. Augustine, Florida, the Castillo de San Marcos also functions as nursery. Started in 1672 and finished in 1695, the Castillo is the oldest fort in the United States. It is now owned by the National Park Service.

The Castillo was built by the Spanish to help defend Florida. They only had one type of stone to use, coquina quarried a half mile away on Anastasia Island. For those not familiar with coquina, I liken it to a granola bar, except that shells, broken and whole, have replaced the oats. Coquina is so soft that cannonballs fired at the fort either bounced off or sank into the stone.

A botanical survey conducted in 2003 and 2004 found 56 plant species, ranging from moss to elm, growing on the coquina walls. Cyanobacteria, nematodes, fungi, and diatoms have also established themselves on the coquina. It is quite a cozy place.

A fern garden growing in coquina

The best place to see to plants is down in the moat, on hanging gardens rich in ferns, grasses, and forbs. The gardens cover the walls every 30 feet or so, wherever water drips from scuppers that drain the courtyard roof. And the plants don’t just grow outside. In one of the courtyard rooms in the 1930s, the park service used to maintain a “fern room” almost completely covered in maidenhair fern. Now only a few ferns grow in this room.

Dark, hanging gardens of the Castillo

The walls are plant rich because the coquina is shell-rich. The heterogeneous mix of shells make a Swiss cheese-like surface, where seeds can land and get established. Water also accumulates in the cavities, further turning the coquina into a nursery.

Despite the beauty of the flowers, maintenance workers at the Castillo constantly pull out the plants by hand. They don’t want the roots to get established and destroy the fort. Cleaning the walls of plants takes about six months, though of course they can’t get it all clean and little fields of color always festoon the mighty fortress.

Wednesday, April 22, 2009

Plants and Stone: The Colosseum

One of my favorite little books about building stone was published in 1855. The author, an erudite English chap named Richard Deakin, turned his attention to the Colosseum, which he called “the most remarkable, the grandest, and the most imposing of all the vast ruins of Ancient Rome.” Deakin reveled in the “noble and graceful animals” who tore “each other to pieces,” and who also made meals of “numberless human beings.” But his real focus was on the plants that had taken over the great structure. In The Flora of the Colosseum, he described 420 species.

For better or worse, the modern Colosseum is a cleaned and sanitized version of its historic past. Gone are the plants that once made the building basically a big nursery. For hundreds of years, flowers, shrubs, and trees sprouted from the travertine and tuff walls. The first list appeared in 1643 and included 336 species, although this historic list does not correspond well with modern names. A study in 1815 dropped the number to 260 but then came Deakin, who appears to have combed every square foot of the Colosseum.

One of Deakin's 420. From Smithsonian Institution Library web site.

Filled with wonderful drawings, the book is also a delight to read. Like the best interpretive writing, Deakin delves into history and science, giving each plant a story, and something for the inquisitive botanist to discover. For example, said plant lover could find cures for dysentery, gout, and rheumatism, dine on strawberries, lettuce, onions, and asparagus, and alleviate the effects of “too great potations” of wine. If you are interested in testing Deakin’s hangover cure, all you have to do is find some Hedera helix, better known as English ivy.

Alas, archaeologists in the 1870s recognized how damaging plants were to the structure and stripped the green mantle. Diversity also decreased with the loss of grazing animals and their contributions to soil fertility. Not all plants have fared poorly in modern times: the most recent floristic study, conducted in 2002, reported that alien species, particularly those associated with humans, have flourished. The 2002 study described 242 species, and total diversity for all studies is 684 species.

Although I understand why workers in Rome remove the plants, I wish they didn’t have to. At least the plants grow fast enough that I can still see this wonderful link between geology and botany.

Tuesday, April 14, 2009

Cobblestones Again: Europe

Several weeks ago, my blog about Seattle cobblestones generated a bit of interest so I thought I would follow up by discussing a few old cobblestone roads from Europe. I am using the term cobble a bit loosely, as technically it refers to a stone ranging in size between 64 and 256 millimeters. Furthermore, cobbles typically are rounded due to ice or water. In this context, a cobble is a stone used as a paving material.

My favorite are the gray cobbles used throughout Rome. Locals call the three-inch-square paving blocks, “San Pietrini,” little Saint Peters, playing on St. Peter’s role as the rock of Christianity. In his landmark De Architectura, or The Ten Books of Architecture, Vitruvius referred to the lava that made the stones as hard, enduring rock, calling it siliceae, or silex.

San Pietrini in La Piazza del Popolo, Rome

More exotic cobbles are found in Seravezza, one of the great localities for marble in Italy. It was here around 1519 that Michelangelo went in search of white marble for the fa├žade he had designed for the church of San Lorenzo in Florence. The church was never built but Michelangelo did open up quarries still used at present. In the sidewalks of Seravezza, you can find a wide variety of the many colors of marble quarried in the Apuan Alps.

Marble paving stones of Seravezza

In the town of Volterra, about 30 miles southwest of Florence, are massive paving stones. Volterra is a classic Tuscan hill town with a history that stretches back to Etruscan times. The Etruscans built several gates, one of which remains and still has figures carved out of basalt, though much weathered. The well-worn roads are made of sediments rich in fossil shells, the largest of which are the size of a deck of cards.

Shells in the road of Volterra

I have not visited my final site of European cobbles. I learned about it from Michael Welland, who writes the blog, Through the Sandglass. Here is what he had to say about the old French Mediterranean city of Narbonne. “Awe-inspiring, the oldest cobbles are the pavement of the great road of the Roman Empire (Narbonne was a major regional capital), the Via Domitia. This section of the road was uncovered not that long ago in the town square. This is really hairs-on-the-back-of-your-neck stuff as you gaze at the wear of traffic 2000 years ago.” He thought they were highly indurated marbles.
Via Domitia (photo courtesy of Michael Welland)

Monday, April 6, 2009

The Unconformity at Yankee Stadium

Recently there has been much bother and brouhaha about the opening of the new stadium for the New York Yankees. The New Yorker’s fine architectural critic Paul Goldberger wrote that the building has “the self important air of a new courthouse built to look as if it had been there since William Howard Taft was President.” Perhaps of more importance, at least to some, Goldberger noted that the stadium “finally [has] sufficient bathroom facilities.” He discussed sight lines, historic homages, and luxury boxes, but what he failed to notice is the unconformity that greets all who enter.

Up close with the Yankees' unconformity (from Wikipedia)

The base of the stadium is a gray, lightly lavender granite quarried from Crotch Island, Maine. Sitting atop it is the Salem Limestone, quarried in Bedford, Indiana, just around the corner from the hole that provided the stone for the Empire State Building. The missing time gap is about 40 million years, a relatively short span considering what could occur in architectural unconformities. (One of my favorites is the three-billion-year gap between the formation of the Morton Gneiss and the deposition of the Kasota Limestone, the two rocks abutting each other on the Art Deco Qwest Building on Minneapolis.)

Such geologic incongruities are common in architecture. Half-billion-year old slates butt against 150,000-year-old travertines. Sandstone that formed in Connecticut sits on top of marble that formed in Italy. Metamorphic rocks interfinger with sedimentary rocks. Fossil-rich, sea-deposited limestones juxtapose mineral-rich, subduction-created granites. The collection of building stones in any downtown area is as complex as any assembled by plate tectonics.

But back to the rock of Yankee stadium. Since the middle 1800s, Maine has been a major source of granite in the building industry. By 1889, Maine had 153 granite quarries, including one in Vinalhaven that employed 1,500 people. Quarries combined good, hard rock with easy transportation. Most of the important quarries were on the islands on the south central coast. Maine granite went into structures throughout the eastern seaboard, such as the Brooklyn Bridge, the U.S. Treasury Building in Washington, D.C., and Boston’s Harvard Bridge. Now, however, only one island quarry remains, the one on Crotch Island, owned by the Deer Isle Granite Company. (If you want to own the same rock as the Yankees, they'll be happy to sell you some.)

Deer Isle granite items for sale from Deer Isle Granite Company

The Deer Isle granite solidified about 371 million years ago, as part of an extensive array of granites that formed during two periods of extension associated with the Acadian Orogeny. The rock on Crotch Island sat at the top of the magma chamber. Unlike other granites within the Deer Isle complex, the Crotch Island has few enclaves and no hornblende. It is one of the lighter colored of Maine’s granites, as well, due mostly to buoyant silicic minerals getting concentrated near the roof of the chamber.

Forty million years after the formation of the Deer Isle rock, a quiet sea covered much of the central part of North America. The hundreds of feet of limestone that developed from the mid-continental sea have been exploited widely as quarries, none more famous than those in and around Bloomington and Bedford, Indiana. The Salem Limestone, often called the Indiana limestone, basically consists of the broken up shells of billions upon billions of marine invertebrates, primarily crinoids, forams, bryozoans, and brachiopods. As I have noted before, it is the most commonly used building stone in America.

Now, I have to admit I am not a Yankees fan. Nor, am I a fan of any baseball team but next time I am in New York, I think I would go out to the ballpark. I wouldn’t actually go to see a game, and if no one was there that would be even better, but I would like to see the unconformity.