Note 10 — XIII

Naglegbeng silicious springs.From here I visited the stalactite springs, not far distant, of Naglegbeng.10 I had expected to see a calcareous fountain, but found the most magnificent masses of silica of infinite variety of form; shallow cones with cylindrical summits, pyramidal flights of steps, round basins with ribbed margins, and ponds of boiling water. One spot, denuded of trees, from two to three hundred paces in breadth and about five hundred in length, was, with the exception of a few places overgrown with turf, covered with a crust of silicious dross, which here and there formed large connected areas, but was generally broken up into flaky plates by the vertical springs which pierced it. In numerous localities boiling hot mineral water containing silica was forcing itself out of the ground, spreading itself over the surface and depositing a crust, the thickness of which depended on its distance from the center point. In this manner, in the course of time, a very flat cone is formed, with a basin of boiling water in the middle. The continuous deposit of dross contracts the channel, and a less quantity of water overflows, while that close to the edge of the basin evaporates and deposits a quantity of fine silicious earth; whence the upper portion of the cone not only is steeper than its base, but frequently assumes a more cylindrical form, the external surface of which on account of the want of uniformity in the overflow, is ribbed in the form of stalactites. When the channel becomes so much obstructed that the efflux is less than the evaporation, the water ceases to flow over the edge, and the mineral dross, during the continual cooling of the water, is then deposited, with the greatest uniformity, over the inner area of the basin. When, however, the surface of the water sinks, this formation ceases at the upper portion of the basin; the interior wall thickens; and, if the channel be completely stopped up and all the water evaporated, there remains a bell-shaped basin as even as if excavated by the hand of man. The water now seeks a fresh outlet, and bursts forth where it meets with the least obstruction, without destroying the beautiful cone it has already erected. Many such examples exist. In the largest cones, however, the vapors generated acquire such power that, when the outlet is completely stopped up, they break up the overlying crust in concentrically radiating flakes; and the water, issuing anew copiously from the center, deposits a fresh crust, which again, by the process we have just described is broken up into a superimposed layer of flakes. In this manner are formed annular layers, which in turn are gradually covered by fresh deposits from the overflowing water. After the pyramid of layers is complete and the outlet stopped up, the water sometimes breaks forth on the slope of the same cone; a second cone is then formed near the first, on the same base. In the vicinity of the silicious springs are seen deposits of white, yellow, red, and bluish-grey clays, overlaying one another in narrow strata-like variegated marl, manifestly the disintegrated produce of volcanic rocks transported hither by rain and stained with oxide of iron. These clays perhaps come from the same rocks from the disintegration of which the silicious earth has been formed. Similar examples occur in Iceland and in New Zealand; but the products of the springs of Tibi are more varied, finer, and more beautiful than those of the Iceland Geysers.