In the first place, the volcanoes of the country discharge both ashes and lava, the latter being most frequently trachytic. Basaltic lavas occur, though less frequently than in Mexico and farther northward; and the columnar structure seen so well at Regla in Mexico is very rare in Guatemala. On the other hand, pumice and obsidian, which are classed with the acid or trachytic lavas, are abundant, the latter furnishing material for knives, while the former has many applications in the arts of the present day. I have seen both basalt and basaltic rapilli in eastern Guatemala near the boundary of San Salvador, and basaltic sand is common on the southern coast. Another feature of the Central American volcanoes is their remarkable regularity of form. This is due to the fact that the emissions consist of ash and lava of slight fluidity. In the Hawaiian Islands, where the basaltic lava is more fluid than in any other volcanic region, the lava-streams often flow for months, and extend fifty or sixty miles from the crater, building by successive eruptions a cone of great diameter in proportion to their height; Mauna Loa having a diameter of ninety miles at the sea-level, with a height of less than fourteen thousand feet and a slope of about seven degrees. The eruptions of the American volcanoes are mainly of masses of rock which are piled regularly about the base, in this way increasing the height, and great quantities of sand which fills the interstices, and finally of lava in a thick, viscid state which clings to the slopes of the growing cone and cements together the sand and larger fragments. No lava-stream, at least of modern times, has been found at any considerable distance from its source. From the specimens I collected in some of the ravines which traverse the older deposits, I saw that in former ages the outflow was not only different from that of modern times, but of great variety of form in contemporaneous streams, although the chemical composition did not vary essentially.