Caisson: In 1890, five screwpiles that had burned or been damaged by ice were replaced with a new kind of lighthouse. These towers were built on caisson foundations. The caisson foundations consisted of a cast iron cylinder sunk deep into the bottom of the Bay and filled with stones and concrete. The tower on top of the caisson foundation was built of iron or brick. Lighthouses built on a caisson foundation are very sturdy and all the caissons built in the Bay have survived. Examples of caisson lights include the Sandy Point Shoal and Smith Point Lighthouses.
Forgotten Beacons: The Lost Lighthouses of the Chesapeake Bay
For more information on lighthouses:
The Chesapeake Chapter of the United States Lighthouse Society, an excellent source of information including photos, history, directions and more.
Chesapeake Bay Lighthouse Project, the result of one couple's quest to visit and photograph all the lights. Terrific site.
Forgotten Beacons: Lighthouses and Lightships of the Chesapeake Bay.