The Gambia less than wide at its widest point, with a total area of . About (11.5%) of the Gambia's area are covered by water. It is the smallest country on the African mainland. In comparative terms, the Gambia has a total area slightly less than that of the island of Jamaica. Senegal surrounds the Gambia on three sides, with of coastline on the Atlantic Ocean marking its western extremity. The present boundaries were defined in 1889 after an agreement between the United Kingdom and France. During the negotiations between the French and the British in Paris, the French initially gave the
Geology of Gambia Geology of Gambia The geology of Gambia is defined by thick and comparatively recent sequences of sediments and sedimentary rocks, deposited in the last 66 million years. The country is underlain almost entirely by geologically recent Cenozoic sedimentary rocks. Much deeper basement rocks are likely present, although they are not well understood. Most research has focused on oil and groundwater exploration. The oldest rock units recognized in the west of the country, along the Gambia River are sandstones and kaolinitic claystones from the Oligocene, Miocene or Pliocene. Ironstone, including iron oxides, gravel, clay and sand dating to the Pleistocene are