The Mystery of the Coral Piers

If you didn’t get a chance to read my last post about our slightly unusual foundation piers, you can check it out here. But to summarize briefly – our old Key West home has been resting on these stone foundation piers for over 100 years (see the photo below). The only thing keeping our house sitting on these piers is gravity – the house is not connected to them whatsoever. We’ve been told by a handful of Key West locals that these stone piers are actually made of coral, and are quite common in Key West. But I was having a difficult time finding information about them. I was trying to find out where they came from, how long they were used this way, and what they’re actually made of.

Two of the foundation piers supporting our home.

Last year I went to the Key West Public Library to research the age of our home. It was there that I was introduced to Tom Hambright, the local expert who works in their History Collection. Since I was having trouble finding info online, I went back to the library to pick Tom’s brain about our foundation piers.

I showed Tom a photo (see below) and he was quick to suggest that they probably aren’t coral, but something called Miami oolite, a variety of limestone. According to Tom, stone like this was mined in a quarry somewhere in the Upper Keys a long time ago. He also thought that this type of stone was mined in quarries on the mainland, and could have been shipped down to the Lower Keys from somewhere around the Miami area.

Foundation piers after they were removed from under the house.

I had never heard of Miami oolite, so upon returning home I did quick online search and hit the jackpot. Many thanks to Mr. Hambright for pointing me in the right direction. As I read about Miami oolite and its history in the Keys, many of the missing pieces started to come together.

I quickly found a series of articles online titled History and Architecture of Old Key West. One article was written by Mr. Hambright himself. In another, titled Architecture of Key West, author George Born describes how Miami oolite came to be used as foundation piers under Key West homes. According to Mr. Born, The region’s natural resources offered limited building materials. South Florida slash pine — Dade County pine — proved to be hard and resistant to decay, but lumbering eventually depleted supply. Soon, builders employed other Southern woods, such as yellow pine, cypress, and cedar. Miami oolite, the bedrock of the Lower Keys, saw use mainly as foundation piers — and only rarely as building stone for whole structures.

I was pleased to stumble across Michael Conchscooter’s blog, Key West Diary. In 2010 he wrote about the Oolite Highway, and begins his blog by stating that Oolite is found in certain parts of the world and the Lower Keys is one of those places. His wasn’t the first site I came across that suggested that oolite is only found in the Lower Keys. Tom Hambright suggested that oolite like this was quarried on the mainland, but the more I’ve read, it seems pretty likely that the oolite supporting my house probably came from the Lower Keys. The piers that were removed from under my house are extremely heavy and it takes at least two people to lift a single block. Considering their weight, it seems likely that the original home builders wouldn’t have wanted to transport these very far, especially 150 years ago. I wouldn’t be surprised if these stones came from Key West somewhere.

A corner pier, visible once the siding and lattice skirting was removed.

My continued research brought me to the NOAA’s website about the Florida Keys where they state that, During the last ice age [the] sea level dropped, exposing the ancient coral reefs and sand bars which became fossilized over time to form the rock that makes up the [Florida Keys] today. The two dominate rock formations in the Keys are Key Largo Limestone and Miami Oolite.

So what exactly is Miami oolite? Is it coral, as I’ve been told my numerous people? Based on what I’ve read (and please correct me if I’m wrong), it’s my understanding that the term coral is a general term used to describe the fossilized rock that forms the present-day Keys. Put simply, the oolite stones that were used as foundation piers under my house are a form of fossilized coral.

Whether you call them coral or oolite, it’s fascinating that these fossilized rocks has been the foundation of my home for almost 150 years. Based on what I’ve read online, it seems clear that the oolite under my house was mostly found in the Lower Keys. It’s probable that it was mined in Key West, and may have even been dug from the ground right where we live.

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