The Marquesas Keys are the only known atoll in the Atlantic. All the
atolls in the Pacific are volcanic in nature. This is not so with this one.
The popular theory is that it is the remains of a meteor crater formed 
many millions of years ago. The cluster of islands are about 4 miles across,
and about 25 miles west of Key West. The lagoon in the middle is shallow
and for the most part impassable. The islands are visited little and probably
look about the same as they did in 1622. When the ill-fated Spanish fleet
loss several ships in the area. The commander of the fleet Marquis de 
Cadereita is where the keys got their name. There are several wrecks in
the area. Huge clusters of coral heads 300 yards off the entire southern side
some shallow enough to run into. Both these boating hazards are marked
on charts of the area.