Page:Popular Science Monthly Volume 2.djvu/248

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236
THE POPULAR SCIENCE MONTHLY.

kind we are pursuing. Now no fragments of lava, not a vestige of it, are to be found there, nor any trace of injury caused by lava. On the contrary, on examining the perpendicular surfaces surrounding this four-sided space, every thing is ashes; 30 or 36 feet deep of ashes; only at the upper part a few bits of coal are seen, ejections from the volcano, layers corresponding with the modern eruptions, and separated by layers of vegetable earth which have had time to be deposited between the several eruptions. Look at the fragments of stuff dug out of one of those caverns—examine them—you will still find nothing in them but ashes, broken up by the pick as readily as clay or pumice.

But it may be asked, How could ashes which are light as dust, and with no coherence, gain hardness enough to take durable impressions, to form supporting arches, and to bear so delusive a look of solidity as to be taken for lava? The ready answer is found in the example of Pompeii, and the casts found in the cellars of Diomed's house; but similar and even more striking cases may help us to understand such power of adhesion. In the valleys of Monte Cavo there are ledges of peperino, formed by the filling up of volcanic ashes mingled with water. This compost grew so dense that the Romans used it for building-material. The Catacombs of Rome, which are nothing else than a volcanic tufa, that is, sand and pulverized fragments, compressed by time and their own weight, are in like manner friable, easy to cut, easier to rub down, and yet galleries are dug in them, arches, ceilings, stairways, numberless tombs, and as many as five stories of excavations, beneath each other! Nor must it be forgotten that pumice, which furnishes so excellent a water-lime, was taken originally from Pozzuola, near Vesuvius, and is nothing more than a ferruginous clay, once subjected to high volcanic temperature, and ejected in a shower of ashes. I recall, too, the great altar at Olympia, described by the traveller Pausanias, which was formed entirely from the ashes of the victims sacrificed to Jupiter. After every sacrifice the priests moistened the ashes with water from the Alpheus, smeared the altar with them, and so enlarged it gradually until, during ten centuries, the structure gained 125 feet in circuit, and 22 in height. Indeed, any one who has seen water flung into a fireplace may judge of the toughness of ashes when mixed with liquids; much more must the volcanic ashes of the Roman Campagna, of Naples and Santorin be suited for making cements.

For the rest, should this explanation only half satisfy the reader, there are the facts, and not to be denied. I defy any careful observer, examining the parts of Herculaneum hitherto brought to light, to discover any thing else in them than ashes. It may be that, on the surface of the existing soil of Portici, which has been raised at least 60 feet, marks of lava-flows are traceable which belong to modern eruptions, especially toward Resina. Neither can I affirm that, in some unexplored quarter of Herculaneum, the presence of lava may not some day