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168 composed of it, and by its brighter colour. It is usually nearly white, often sufficiently hard and dense to work well, as a beautiful building material, capable of a good polish; but also passing insensibly, within a few miles, into a soft, sandy stuff, of little coherence, like a compound of English chalk, and fine white Dorsetshire sand, but still forming rocky eminences several hundred feet in height.

Upon this again appear to lie, chiefly in the bottoms and on the flanks of the valleys, beds of marls of various tints, of enormous thickness—600 or 700 feet in some places. These I presume to be the sub-Apennine marls of Collegno.

In the lowermost portion of these marls, beds of yellow and brown sandstone occur, here and there of great thickness; in some places, they are traversed by beds of indurated, highly ferruginous and magnetic, dark gray calcareous rock,—by beds of gypsum,—and in very many places, give evidence of metamorphism. The beds, usually soft and sectile, and acted on with immense rapidity by river erosion, being converted into masses of striped jasper, often of great beauty and extreme hardness.

In the neighbourhood of Potenza, there are large developments of indurated argillaceous slaty beds, of dark blue gray colour, which Collegno appears to refer to these sub-Apennine marls, but which appeared to me widely different, in lithological character at least, from those last referred to.

Above these marls, reposes, the usually great depth of alluvial clays, which constitute the valley bottoms. The tops and flanks, of the upper and lower limestone mountains, are almost always nearly bare of soil; it has