The great distance from the sea of the volcanoes of the interior of Asia is a remarkable and solitary phenomenon. Abel Rémusat, in a letter to Cordier (Annales des Mines, T. v. 1820, p. 137), first directed the attention of geologists to this fact. The distance, for example, in the case of the volcano of Pe-schan, to the north, or to the Icy Sea at the mouth of the Obi, is 1528 geographical miles; to the south, or to the mouths of the Indus and the Ganges, 1512 geographical miles; to the west, 1360 geographical miles to the Caspian in the Gulf of Karaboghaz; and to the east, 1020 geographical miles to the shores of the sea of Aral. The active volcanoes of the New World were previously supposed to offer the most remarkable instances of such phenomena at a great distance from the sea; their distance, however, is only 132 geographical miles in the case of the volcano of Popocatepetl in Mexico, and only 92, 104, and 156 geographical miles in those of the South American volcanoes Sangai, Tolima, and de la Fragua, respectively. I exclude from these statements all extinct volcanoes, and all trachytic mountains which have no permanent connection with the interior of the earth. (Asie Centrale, T. ii. p. 16-55, 69-77, and 341-356.) East of the volcano of Turfan, and of the fertile Oasis of Hami rich in fine fruit, the chain of the Thian-schan gives place to the great elevated tract of Gobi which follows a S.W. and N.E. direction. This interruption of the mountain chain, caused by the transverse intersection of the Gobi, continues for more than 9-1/2 degrees of longitude; but beyond it the mountains recommence in the somewhat more southerly chain of the In-schan, or the Silver Mountains, running (north of the Pe-tscheli) from west to east almost to the shores of the Pacific near Pekin, and forming a continuation of the Thian-schan. As I have viewed the In-schan as an easterly prolongation (beyond the interruption of the Gobi) of the cleft above which the Thian-schan stands, so one might possibly view the Caucasus as a westerly prolongation of the same, beyond the great basin of the Aral and Caspian Seas or the depression of Turan. The mean parallel of latitude or axis of elevation of the Thian-schan oscillates between 40-2/3° and 43° N. lat.; that of the Caucasus, according to the map of the Russian Etat-Major (running rather E.S.E. and W.N.W.), is between 41° and 44° N. lat. (Baron von Meyendorff, in the Bulletin de la Societé géologique de France, T. ix. 1837-1838, p. 230.) Of the four parallel chains which traverse Asia from east to west, the Thian-schan is the only one in which no summits have yet had their elevation above the sea determined by measurement.