Nor is the imagination disappointed when the interior of the crater is seen for the first time. I have already described the impression which that view produced upon us, entering it from the east. The lake fills almost the whole of the western half of its area, at a level of 7656 feet. The remaining portion consists of older lava streams, covered with pumice, and of some more recent, which bristle with sharp crags. The eastern shore of the lake is deeply indented, and the volcanic matter has cooled in the form of high banks. The figure described by the walls of the crater is almost exactly circular, the diameter being greatest along an east-north-east line, or between the fork, where we first entered the basin, and the passage in on the west (c and m on plan). The distance between these points is nearly 5 miles (8500 yards). Nimrud is therefore one of the largest perfect craters in the world. [250] The period during which it seethed with a lake of molten matter, which overflowed into the lower levels on every side, must date far beyond the limits of history. At the present day not a wreath of smoke ascends from the volcano; though at times a little landslip sends the fine sand into the air, with much the same appearance as a cloud. But the student of volcanic phenomena could not select a better example of the successive stages of eruptive activity. In an earlier stage we must suppose the walls of the crater somewhat higher, and the area considerably narrower which they enclosed. The earliest lavas, in the case of Nimrud, were of an acid and viscous description (rhyolitic augite-andesites); and, as often as they rose above the lip of the caldron, they did not flow very far. But the later basaltic lavas had a larger extension; and to them is due, in no small measure, the plateau on the east of Tadvan, which acts as a dam to the lake of Van. The molten lava surged against the precipices which confined it, and gradually wore them back. The work of enlargement was advanced by violent explosions, which were principally directed against the western and eastern sides of the volcanic basin. The uppermost and steepest portions of the wall were, on these two sides, completely blown away. This epoch in the life of the volcano, the storm and stress of a tumultuous youth, was followed by the gradual subsidence of its energies. The streams of lava were confined to the interior of the crater, and the deeper portion came to be covered with a lake. It was perhaps at this period that were produced the little craters which figure on the outer slopes of the principal caldron, roughly along meridional lines. Such minor points of emission were also formed within that caldron, and from them proceeded some of the older flows which cover its floor. Explosions again occurred; but their effects were only local. They blew away portions of the little craters, and sent up showers of dust, which, falling to the ground, cloaked the surface of the lava streams.