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The enduring pyramids themselves are formed of the nummulitic limestone studded with its "Pharaoh's beans," the exuviæ of shell-fish that perished ages before the Nile had created Egypt. Of the breccias there is a great variety among the relics of ancient Rome. A breccia is a rock made up of angular pebbles or fragments of other rocks.
He remarks that similar breccias with slickensides are observed on a minor scale where rocks of different composition and rigidity are contorted together. Such protrusion may have been brought about by degrees by innumerable shocks of earthquakes repeated after long intervals of time along the same tract of country.
The hollows in some of the fragments of vesicular lava of which the breccias and conglomerates are composed are partially filled with calc-sinter, being thus half converted into amygdaloids.
The prevailing colour of the fragments is that of a dark brown intermixed with others of smaller size, of red, green, blue, white, purple, bright yellow, and sometimes black, all harmonising together most beautifully. The comparatively small pieces found at Tivoli now adorn the Churches of St. Andrea della Valle, famous for its rich varieties of breccias, St.
Along with the breccias which I have thus incidentally noticed, but to which a whole essay might be devoted on account of their beauty, rich variety, and great value and rarity, should be classified a kind of "breccia dure," called Breccia d' Egitto.
Probably the most beautiful of all the ancient breccias is that called Breccia della Villa Adriana, from its occasional occurrence in the ruins of Hadrian's Villa, and also Breccia Quintilina, from its having been found in the grounds of the magnificent Villa of Quintilius Varus, commemorated by Horace, at Tivoli, now occupied by the Church of the Madonna di Quintigliolo.
The derivation of the water and the exact mode of eruption are difficult to determine.... Towards the summits the breccias gradually lose their stratified character and become more firmly cemented. Over large areas in the Truckee quadrangle the andesite masses consist of breccias containing numerous dykes and necks of massive andesite....
This basin has been burst through and filled up in many parts by eruptive traps and breccias, which often bear in their substances angular fragments of the more ancient rocks, as shown in the fossils they contain.
Volcanic rocks of this stage are only known in Ireland, on the borders of Cos. Mayo and Galway, west of Lough Mask, and at the extreme headland of the Dingle Promontory in Co. Kerry. They consist of porphyrites, felstones and tuffs, or breccias, contemporaneously erupted during the Wenlock and Ludlow stages.
After the filling up or drainage of the ancient lakes, huge piles of trachytic and basaltic rocks, with volcanic breccias, accumulated to a thickness of several thousand feet, and were superimposed upon granite, or the contiguous lacustrine strata.
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