Between the Gulfs of Guayaquil and Panama, north-east of the cold current, the temperature of the sea during the month of April rose as high as 24°·5, (87°·12 Fahr.). Within the range of the current, Mr. Dirckinck had carried on his observations in compliance with my instructions, by means of thermometers that had been compared by Arago. Everywhere in the current, in December 1824, he found from 16° to 18° (68° to 72°·5 Fahr.); between Quilca and Callao, in January, 1825, from 18° to 19° (72°·5 to 74°·75 Fahr.); between Chorillos, near Lima (Lat. 12° 39' S.) and Valparaiso, in August, 1825, from 13°·8 to 10°·5 (63°·05 to 55°·62 Fahr.); between Chorillos and San Carlos de Chiloe, in June, 1825, from 18°·8 to 9°·2 (74°·3 to 52°·7). In sailing from the Sandwich Islands to the west coast of America, the Imperial Expedition will have to choose between the Ports of San Francisco or Acapulco. The first choice would be of great mineralogical advantage for those regions of the United States, lying North of the river Gila.[3] Parallel with the chain of the Rocky Mountains, which, according to Marcou, contains up to the present day several volcanoes in full activity in its northern part (Lat. 46° 12' N.), run single, and at certain points double ranges of coast chains from San Diego to Monterey, from 32° 15' N. to 46° 45' N. They begin with the coast range specially so-called, which is a continuation of the high ridge of the Peninsula of Lower or Old California; after which, farther to the North, there follow in succession, first the Sierra Nevada di Alta California, between 36° and 38° N. the lofty Shasty mountains, and the Cascade Range, nearly twenty six miles distant from the littoral, including many high and active volcanoes, and extending far beyond Fuca Straits. The following are still in eruption:--Mount St. Elias (46° 2' N.); Mount Regnier, or Rainier, (46° 46'); and Mount Baker, (48° 48'.) These three active cones would be most conveniently visited by the geologist of the expedition from San Francisco, as would likewise the whole Cascade Range. We have as yet no certain intelligence as to the geology of the entire longitudinal auriferous valley of the Sacramento River, (where a trachytic crater, in a state of disintegration, is known as the Butt of Sacramento). Does the auriferous quartz occur in veins, and are these still _in situ_, or are they broken up? What description of rock is traversed by these veins? Does the wash-gold here contain occasionally, as in the Ural Mountains, fragments of vein-stones with isolated cavities, in which are found impressions of leaves and membranes, clearly proving that they have not been rolled, or transported by water, any great distance to the spot they now occupy? Have these been found, alongside of gold, diamonds, platinum, osmium, iridium, or mercury? [Footnote 3: The Gila falls into the Colorado about forty miles above the embouchure of the latter into the head of the Gulf of California.]