_Tiburon_ is the largest of these, and appears to be about sixty miles in length. Off the shore of the intendancy of Guadalaxara is the islet of _Isabella_ in 21° 50ʹ north latitude, and 105° 56ʹ west longitude. Islet of _Juanico_ in 21° 45ʹ north latitude, and 107° 41ʹ west longitude. _Piedra Blanca_ at the mouth of the Rio Grande de Santiago, and in the port of San Blas, in 21° 33ʹ and 105° 17ʹ west longitude. _Las Tres Marias_ abounding with wood, water, salt-pits and game, which cause them to be frequented by the English and American whalers; the French and English pirates used to winter in them, when they cruised in the South Seas. The south cape of the easternmost island is in 21° 16ʹ north latitude, and 106° 17ʹ west longitude. They were named Islands de la Magdalena, by Diego de Mendoza in 1532, and are occasionally visited by the Spaniards from Saint Blas, for the flax and lignum vitæ they produce. South of these, and near cape Corrientes, is the islet Isasvirivil in 20° 45ʹ north latitude, and 105° 57ʹ west longitude. The Revillagigedo islands, which are a considerable distance from the coast, are four in number. Santa Rosa, Socorro, Rocca Partida, and San Benedito; their origin seems to be volcanic, as pumice stones are found in them; _Santa Rosa_ is in 18° 37ʹ north latitude, 114° 3ʹ west longitude. _Socorro_, the highest summit of which is more than 3657 feet above the sea, is the largest of the group, but not above fifteen or twenty miles broad and long, and is situated in 18° 48ʹ north latitude, 110° 9ʹ west longitude. _Rocca Partida_ is in 19° 4ʹ north latitude, 111° 5ʹ longitude. _San Benedito_ in 19° 18ʹ north latitude, and 110° 53ʹ west longitude. Socorro was visited by Captain Collnett, on the 20th September, 1793. He afterwards saw other islands of this group.