A couple of years ago, while visiting Cat Island in the Bahamas, I
accompanied a group of dive writers to an inland blue hole.  It was August
and hot as hell.  We had to hike the last half mile or so through the bush.
The terrain made it very difficult going, think of giant craggy Swiss cheese
made of rock.  Evil potholes, deep with sharp edges.  The blue hole itself
glowed like a swimming pool. The surface area was maybe 200 feet across and
100 yards long.  The water was edged with the same sharp dangerous rock as
the trail had been.  Like a swimming pool, the hole had a shallow end and and
a deep end, only the deep end was a cave, a sharply-angled tunnel that went
down god only knows how many hundreds of feet.

I hadn't meant to dive.  I have neither cave nor cavern training.  But it was
so hot that I did go snorkeling.  There wasn't much relief from the heat in
the shallow water.  You could have poached an egg in it.  And it was salty,
saltier than a pretzel.  I didn't have any way of measuring the salinity
other than taste, but I'd been diving in the ocean all week and this was much
saltier. REALLY salty.

There were thousands of oysters in that blue hole, paper-thin flat oysters.
They were small, most of them no more than an inch and a half long and maybe
an inch wide.  I'm no expert, but they looked to me a lot like the clump of
tree oysters illustrated on page 203 of the Golden Books Seashells of North
America.

I finally did get to cool off.  Swimming over the cave, I found the exhaust
bubbles from the divers below brought up the cool water from down the cave.
Now I know how a strawberry feels in a flute of chilled champagne.