the less elevated central area, had been separated from it by irregularly curved faults, the strata would have been tilted seaward, and a “Crater of elevation,” like that of St. Jago or that of Mauritius, but of much vaster dimensions, would have been formed. I will only further remark, that the frequent occurrence of extensive lakes at the foot of large volcanoes, and the frequent association of volcanic and fresh-water strata, seem to indicate that the areas around volcanoes are apt to be depressed beneath the level of the adjoining country, either from having been less elevated, or from the effects of subsidence.) We might expect, from what we see along ordinary faults, that the strata on the upraised side, already dipping outwards from their original formation as lava-streams, would be tilted from the line of fault, and thus have their inclination increased. According to this hypothesis, which I am tempted to extend only to some few cases, it is not probable that the ring would ever be formed quite perfect; and from the elevation being slow, the upraised portions would generally be exposed to much denudation, and hence the ring become broken; we might also expect to find occasional inequalities in the dip of the upraised masses, as is the case at St. Jago. By this hypothesis the elevation of the districts in mass, and the flowing of deluges of lava from the central platforms, are likewise connected together. On this view the marginal basaltic mountains of the three foregoing islands might still be considered as forming “Craters of elevation;” the kind of elevation implied having been slow, and the central hollow or platform having been formed, not by the arching of the surface, but simply by that part having been upraised to a less height. CHAPTER V. GALAPAGOS ARCHIPELAGO. Chatham Island. Craters composed of a peculiar kind of tuff. Small basaltic craters, with hollows at their bases. Albemarle Island; fluid lavas, their composition. Craters of tuff; inclination of their exterior diverging strata, and structure of their interior converging strata. James Island, segment of a small basaltic crater; fluidity and composition of its lava-streams, and of its ejected fragments. Concluding remarks on the craters of tuff, and on the breached condition of their southern sides. Mineralogical composition of the rocks of the archipelago. Elevation of the land. Direction of the fissures of eruption. (FIGURE 11. MAP 3. GALAPAGOS ARCHIPELAGO. Showing Wenman, Abingdon, Bindloes, Tower, Narborough, Albemarle, James, Indefatigable, Barrington, Chatham, Charles and Hood’s Islands.)