The great distance of the volcanoes of the interior of Asia from the sea coast is a remarkable and isolated phenomenon. Abel Rémusat, in a letter to Cordier[BU], first directed the attention of geologists to this fact. This distance, for instance, in the case of the volcano of Pe-schan, from the north or the Icy Sea at the mouth of the Obi, is 1528 miles; and from the south or the mouths of the Indus and the Ganges, 1512 miles; so central is the position of fire-emitting volcanoes in the Asiatic continent. To the west its distance from the Caspian at the Gulf of Karuboghaz, is 1360 miles, and from the east shores of the Lake of Aral, 1020 miles. The active volcanoes of the New World had hitherto offered the most remarkable examples of great distance from the sea coast, but in the case of the volcano of Popocatepetl, in Mexico, this distance is only one hundred and thirty-two miles, and only ninety-two, one hundred and four, and one hundred and fifty-six, respectively in the South American volcanoes Sangai, Tolima, and de la Fragua. All extinct volcanoes, and all trachytic mountains, which have no permanent connexion with the interior of the earth, have been excluded from these statements[BV]. East of the volcano of Turfat, and of the fruitful Oasis of Hami, the chain of the Thian-schan merges into the great elevated tract of Gobi, which runs in a S.W. and N.E. direction. This interruption of the mountain chain continues for more than 9½ degrees of longitude; it is caused by the transversal intersection of the Gobi, but beyond the latter, the more southern chain of In-schan (Silver Mountains), proceeding from west to east, to the shores of the Pacific near Pekin (north of the Pe-tscheli), forms a continuation of the Thian-schan. As we may regard the In-schan as an eastern prolongation of the fissure from which the Thian-schan is upheaved, so we may also be inclined to consider the Caucasus as a western prolongation of the same range, beyond the Great Aralo-Caspian basin or of the lowlands of Turan. The mean parallel or axis of elevation of the Thian-schan oscillates between 40° 40′ and 43° north latitude; that of the Caucasus (inclining, according to the map of the Russian Staff, from E.S.E. to W.N.W.) between 41° and 44°.[BW] Of the four parallel chains that traverse Asia, the Thian-schan is the only one of which no summit has as yet been measured.