The great eruptions of the Icelandic Geysers are, it has been observed, accounted for by the siphon theory; in other words, this theory supposes the existence of a chamber in the heated earth, not quite full of water, and communicating with the upper air by means of a pipe, whose lower orifice is _at the side_ of the cavern and _below_ the surface of the water. The water, being kept boiling by the intense heat, generates steam, which soon accumulates such force as to discharge the contents of the pond into the air through the narrow vent, or, at least enough to allow of the escape of the superfluous steam. In the Great Geyser of Iceland this eruption occurs with tremendous power, lasting only a few moments, when, all the volume of water falling back into the pool, it sinks much below its ordinary level, and remains quiescent for several days, until a fresh creation of steam repeats the phenomenon. 'The Witches' Caldron,' which is the 'Great Geyser' of California, on the contrary, never rises into the air; the subterranean pond of which it is the safety valve, may be considered to rise in it, as in a pipe, to the surface. It is not necessary to suppose a siphon; a straight pipe, communicating with the air, will account for all that is peculiar to this hot spring. Before attempting to describe the wonders of the 'Devil's Canon,' it may be well to give some account of the Geysers of Iceland, to render this essential difference in character the more striking, especially as numerous theories, professing to account for the Californian phenomena, have been propounded by the people of that State, none of which are thoroughly satisfactory to any one who has examined them attentively. The following is taken from 'Letters from High Latitudes,' which appeared in 1861, and is only one of many accounts by Iceland travellers. Those interested in these matters will derive much information from the sketches of Mr. J. Ross Browne, which have had many readers through _Harper's Magazine_. We quote: 'I do not know that I can give you a better notion of the appearance of the place than by saying that it looked as if for about a quarter of a mile the ground had been honey-combed by disease into numerous sores and orifices; not a blade of grass grew on its hot, inflamed surface, which consisted of unwholesome-looking, red, livid clay, or crumbled shreds and shards of slough-like incrustations. Naturally enough, our first impulse on dismounting was to scamper off to the Great Geyser. As it lay at the farthest end of the congeries of hot springs, in order to reach it we had to run the gauntlet of all the pools of boiling water and scalding quagmires of soft clay that intervened, and consequently arrived on the spot with our ankles nicely poulticed. But the occasion justified our eagerness.