In the previous blog entry about the ancient Lucayan tool that I found, I was struck by a line in the historical intrepretive sign that I saw in the national park. The sign said that the Arawak and Lucayan Indians were forced to use coral, because they didn't have access to hard rocks.
When I got to thinking about it, it was strange to me. I come from a country were rock cuts are common, and the very hard metamorphic and igneous rocks are common. They make up the hills that we live in, and every road has a rock cut every few miles. But these islands are made of limestone -- dead coral reefs. This limestone bubbles when you drop some vinegar on it. It is just like the scales in your kettle, except a lot more of it.
There are two types of limestone bedrock. The first is dead coral reefs. The second is beach rock made from centuries of beach sand being compacted by the waves. I read somewhere that most of the sand on the beach is made by fishes such as parrotfish, who chomp on the limestone coral and excrete sand. They have been doing this for thousands of years, and when you combine the action of the waves, you get the beautiful sand beaches.
But as for the island, every once and a while you can see the bedrock of limestone. There isn't much soil, so you don't have to dig far. Plants can grow in the cracks of the limestone nicely (see inset). And when it is cut for a road, you can see the pattern (main picture) of limestone being laid down over the centuries. Yet chip a small piece off and throw it in vinegar and it dissolves. Thank goodness that the oceans are not made of vinegar, otherwise we would be in a real pickle.