From Sir G. Mackenzie's Travels in Iceland.

"The hot springs in the valley of Reikholt, or Reikiadal, though not the most magnificent, are not the least curious among the numerous phenomena of this sort that are found in Iceland. On entering the valley, we saw numerous columns of vapour ascending from different parts of it. The first springs we visited, issued from a number of apertures in a sort of platform of rock, covered by a thin coating of calcareous incrustations. From several of the apertures the water rose with great force, and was thrown two or three feet into the air. On plunging the thermometer into such of them as we could approach with safety, we found that it stood at 212°.

"A little further up the valley, there is a rock in the middle of the river, about ten feet high, twelve yards long, and six or eight feet in breadth: from the highest part of this rock a jet of boiling water proceeded with violence; dashing the water up to the height of several feet. Near the middle, and not more than two feet from the edge of the rock, there is a hole, about two feet in diameter, full of water boiling strongly. There is a third hole near the other end of the rock, in which water also boils briskly. At the time we saw these springs, there happened to be less water in the river than usual, and a bank of gravel was left dry a little higher up than the rock. From this bank a considerable quantity of boiling water issued.

"About a mile further down, at the foot of the valley, is the Tungahver, an assemblage of springs the most extraordinary, perhaps, in the whole world. A rock (waoke?) rises from the bog, about twenty feet, and is about fifty yards in length, the breadth not being considerable. This seems formerly to have been a hillock, one side of which remains covered with grass, while the other has been worn away, or perhaps destroyed at the time when the hot water burst forth. Along the face of the rock are arranged no fewer than sixteen springs, all of them boiling furiously, and some of them throwing the water to a considerable height. One of them, however, deserves particular notice. On approaching this place, we observed a high jet of water near one extremity of the rock. Suddenly this jet disappeared, and another, thicker but not so high, rose within a very short distance of it. At first we supposed that a piece of the rock had given way, and that the water had at that moment found a more convenient passage. Having left our horses, we went directly to the place where this had apparently happened; but we had scarcely reached the spot, when this new jet disappeared, and the one we had seen before was renewed. We observed that there were two irregular holes in the rock, within a yard of each other; and while from one a jet proceeded to the height of twelve or fourteen feet, the other was full of boiling water. We had scarcely made this observation, when the first jet began to subside, and the water in the other hole to rise; and as soon as the first had entirely sunk down, the other attained its greatest height, which was about five feet. In this extraordinary manner, these two jets played alternately. The smallest and highest jet continued about four minutes and a half, and the other about three minutes. We remained admiring this very remark-able phenomenon for a considerable time, during which we saw many alternations of the jets, which happened regularly at the intervals already mentioned.

"I have taken the liberty to give a name to this spring, and to call it 'The Alternating Geyser.'

"These springs have been formerly observed, though the singularity of the alternations does not seem to have been attended to as any thing remarkable. Olafson and Paulson mention, that the jets appear and disappear successively, in the second, third, and fourth openings. We observed no cessations in any of the springs, except in the two under consideration.

"To form a theory of this regular alternation is no easy matter; and it seems to require a kind of mechanism very different from the simple apparatus usually employed by nature in ordinary intermittent or spouting springs. The prime mover in this case is evidently steam, an agent sufficiently powerful for the phenomena. The two orifices are manifestly connected; for, as the one. jet sinks towards the surface, the other rises, and this in a regular and uniform manner. 1 observed once, that when one of the jets was sinking, and the other beginning to rise, the first rose again a little before it was quite sunk down, and then when this happened, the other ceased to make any efforts to rise, and returned to its former state, till the first again sunk, when the second rose and played as usual. This communication must be formed in such a manner, that it is never complete, but alternately interrupted, first on one side, and then on the other. To effect this without the intervention of valves, seems to be impossible; and yet it is difficult to conceive the natural formation of a set of permanent valves: so that this fountain becomes one of the greatest curiosities ever presented by nature, even though, in attempting to explain the appearances it exhibits, we take every advantage that machinery can give us. If it is occasioned by natural valves, these must be of very durable materials, in order to withstand the continual agitation and consequent attrition."