Bahama Banks

[1][2] The limestone that comprises the Banks has been accumulating since at least the Cretaceous period, and perhaps as early as the Jurassic; today the total thickness under the Great Bahama Bank is over 4.5 kilometres (2.8 miles).

[3] As the limestone was deposited in shallow water, the only way to explain this massive column is to estimate that the entire platform has subsided under its own weight at a rate of roughly 3.6 centimetres (2 inches) per 1,000 years.

[4] The slopes around them however, such as the border of the Tongue of the Ocean in the Great Bahama Bank, are very steep.

The Banks were dry land during past ice ages, when sea level was as much as 120 meters (390 feet) lower than at present; the land area of the Bahamas today thus represents only a small fraction of their prehistoric extent.

[3][4] When they were exposed to the atmosphere, the limestone structure was subjected to chemical weathering that created the caves and sinkholes common to karst terrain, resulting in structures like blue holes.

The Bahama Banks: Little Bahama Bank in the north, Great Bahama Bank in the south, and Cay Sal Bank in the west; and the Caicos Bank of the Turks and Caicos Islands in the east
Map of 1888 showing the banks of the Lucayan Archipelago from Navidad Bank or Bajo Navidad north of the Dominican Republic in Hispaniola to Little Bahama Bank in The Bahamas