though hardened by fire, are crumbled into dust, whilst the masses of travertine around it, though formed by a variable source from the most perishable materials, have hardened by time, and the most perfect remains of the greatest ruins in the eternal city, such as the triumphal arches and the Colosaeum, owe their duration to this source.  Then, from all we know, this lake, except in some change in its dimensions, continues nearly in the same state in which it was described 1,700 years ago by Pliny, and I have no doubt contains the same kinds of floating islands, the same plants, and the same insects.  During the fifteen years that I have known it it has appeared precisely identical in these respects, and yet it has the character of an accidental phenomenon depending upon subterraneous fire.  How marvellous then are those laws by which even the humblest types of organic existence are preserved though born amidst the sources of their destruction, and by which a species of immortality is given to generations floating, as it were, like evanescent bubbles, on a stream raised from the deepest caverns of the earth, and instantly losing what may be called its spirit in the atmosphere.”  These last observations of the stranger recalled to my recollection some phenomena which I had observed many years ago, and of which I could then give no satisfactory explanation.  I was shooting in the marshes which surround the ruins of Gabia, and where there are still remains supposed to be of the Alexandrine aqueduct; I observed a small insulated hill, apparently entirely composed of travertine, and from its summit there were formations of tufa which had evidently been produced by running water, but the whole mass was now perfectly dry and encrusted by vegetables.  At first I suspected that this little mountain had been formed by a jet of calcareous water, a kind of small fountain analogous to the Geiser, which had deposited travertine and continued to rise through the basin flowing from a higher level; but the irregular form of the eminence did not correspond to this idea, and I remained perplexed with the fact and unable to satisfy myself as to its cause.  The views of the stranger appeared to me now to make it probable that the calcareous water had issued from ancient leaks in the aqueduct and formed a hillock that had encased the bricks of the erection, which in other parts, where not encrusted by travertine, had become entirely decayed, degraded, and removed from the soil.  I mentioned the circumstance and my suspicion of its nature.  The stranger said:  “You are perfectly correct in your idea.  I know the spot well, and if you had not mentioned it I should probably have quoted it as an instance in which the works of art are preserved, as it were, by the accidents of Nature.  I was so struck by this appearance last year that I had the travertine partially removed by some workmen, and I found beneath it the canal of the aqueduct in a perfect state, and the bricks