The exhibition of comprehensive volcanic collections brings to light the strong analogy subsisting between the trachytes belonging to volcanoes, far distant from one another, while it indicates the existence of great differences in the mineralogical composition of volcanoes situated very near each other. My most excellent friend and fellow-traveller in Siberia, Professor Gustavus Rose, recently subjected the trachytes of the Berlin Museum, the greater number of which were collected by myself, to careful crystallographical and chemical investigation. He found oligoclase and pyroxene on the trachytes of Chimborazo, Popocatepetl, Colima, Tunguragua, Puracé, Paramo de Ruiz, and the Peak of Teneriffe, which has recently been accurately examined by Mr. Charles Deville. The trachytes of Toluca, Orizaba, Gunung Barang, and Burung Agung, on the Island of Java, Argæus, in Asia Minor, Cuneguilla, south of Sta. Fé de Nuevo-Mexico, the Sièrra de San Francisco, west of the Rocky Mountains and Pueblo Zuni, consist of hornblende, oligoclase, and brown mica. The trachytes of Stromboli and Etna, those of the Siebengebirge (Drachenfels), and of Kara Hissar in Phrygia, consist of large crystals of glassy felspar, with numerous smaller crystals of oligoclase, some hornblende and mica. Oligoclase, having been mistaken for albite, led to the fantastic idea of a peculiar rock, the _Andesite_, prevailing in the Andes, and even led our great master, Leopold von Buch, to make some curious distinctions, (Déscription des Iles Canaries, 1836, pp. 186-87.) To ascertain the average height above the level of the sea, I propose that furrows should be cut in the rocks of the different regions along with inscriptions, which might carry information to unborn ages, as has been done, on my suggestion, now some 25 years ago, by the Academy of Science at St. Petersburg, on the Caspian Sea, while Sir James Ross, in his "Voyage of Discovery in the Southern and Antarctic Regions," 1839-43, Vol. II. p. 23, regrets not having done so, or, at least, of having only once adopted this plan.