The history of individual key names in the Dry Tortugas group is very confusing. The Dry Tortugas Keys, being formed totally of sand, have formed, shifted, disappeared, and reformed over the years as a result of storms and currents. See individual key names above for details. The Dry Tortugas Keys may be the most historically significant of the keys, It is generally believed that they were visited by Ponce de Leon in 1513, and they appear on nearly every chart and map since that time. In 1742, the British warship H.M. S. Tyger grounded and sunk here. 242 British sailors were marooned as a result (probably on Garden Key) and survived for more than two months by eating sea turtles, seals and fish. They built several small fortifications using timbers and cannons salvaged from the wreck, and finally escaped back to Jamaica by building a sloop from the wreckage, and using the sloop to capture a passing Spanish schooner. The first lighthouse in the Dry Tortugas was on Garden Key, and was first lighted in 1826. In 1858 a second lighthouse was built on Loggerhead Key (II).