are produced by the oxides of iron which the water carries with it in its infiltration through the intervening strata.  They are very soft and perishable, and consequently are very rarely found among the ruins of ancient Rome.  The Oriental alabasters, on the other hand, which are distinguished from the European by their superior hardness and durability, are in reality not sulphates, but carbonates of lime.  Their hardness is quite equal to that of the best statuary marbles.  The ancient quarries on the hill—­the modern Mount St. Anthony—­near the town of Alabastron, in Middle Egypt, from which the material got its name, have only recently been re-opened, but blocks of large size and perfect beauty have been obtained.  Owing to the facility with which alabaster can be reduced by fire to lime, very few large examples of it in Rome have escaped the ruthless kilns of the middle ages.  The most interesting specimens of ancient alabaster are the very beautiful vase of Alabastro cotognino, prolate in form, and in colour white, streaked with very light pink, which contained the ashes of Augustus, found in the ruins of his mausoleum, and now in the Vatican; the bust of Julius Caesar, made of the variety tartaruga, from the resemblance of its brownish-yellow markings to tortoise-shell, in the Museum of the Capitol; and the two large blocks of alabastro a pecorella, brought from the Villa of Hadrian, in the fourth portico of the Vatican, the largest and most beautiful specimens of this very rare alabaster in Rome, distinguished by white circular blotches, like a flock of sheep huddled together, on a deep blood-red ground.  In the churches there are numerous specimens of all the varieties, forming the columns and sheathings of altars, memorial chapels, and monuments; the incrustations of alabaster on the walls of the Borghese chapel, in Santa Maria Maggiore, being conspicuous for their splendid effect.  The baldacchino above the high altar of St. Paul’s is supported by four splendid columns of Oriental alabaster presented to Gregory XVI. by Mehemet Ali, the viceroy of Egypt.  An interesting collection of beautiful and valuable varieties of alabasters may be made in connection with the building operations still carried on in the unfinished facade of the basilica fronting the Tiber.

The well-known Verde antico is not a marble, but a mixture of the green precious serpentine of mineralogists and white granular limestone.  It may also be called a breccia, for it is composed of black fragments, larger or smaller, derived from other rocks, whose angular shape indicates that they have not travelled far from the spots where they occur.  The ancient Romans called it Lapis Atracius, from Atrax, a town in Thessaly, in the vicinity of which it was found.  It can hardly be distinguished, except by experts, from the modern green marbles of Vasallo in Sardinia, and Luca in Piedmont.  It occurs somewhat abundantly in Rome, having been a