Category: StreetSmartNaturalist

Boston: Where it All Started

I moved to Boston about a dozen years ago. My wife and I had been living in Moab so it was quite a shock to arrive in the Hub. Gone were the wonderful red rock canyons, wide open spaces, and 12,000 foot high mountain peaks. Instead, I found concrete canyons, urban density of almost 20,000 people per square mile (compared with less than 2 around Moab), and minimal topography. I was not happy until I discovered the mosaic of geology used to construct the city’s buildings: sandstone, granite, travertine, marble, puddingstone, and gneiss.


As I have now discovered, Boston, like most big cities, is built with a range of rocks equal to any assembled by plate tectonics. With a short walk you can find rocks ranging in age from 3.5 billion years old to less than 200,000 years old. There are rocks from every continent except Antarctica. Plus, builders often go to the effort of polishing the rocks, so it is even easier to see the wonderful structures, fossils, and minerals. There were many times I wish I had my rock hammer and a bottle of acid.

I bring this up because today in the Boston Globe there is an article of mine about the great rocks of Boston. Based on a timeline, the story highlights 13 buildings and their geologic and cultural stories. The editor and designer did a great job. I have only one regret, at this point it’s not on-line, or if it is I cannot find it, so if anyone out there sees it could you let me know how it looks.

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.