Page:Great Neapolitan Earthquake of 1857.djvu/534

428 This may be viewed as about the lowest level of the Piano Mattine, so that its mean level is nearly the same, as that of the great Piano of Diano.

For some miles about the junction of the Moglia and Agri, evidences of prodigious river erosion exist. In many places in the main river-bed—here from 500 to 700 feet, or upwards, in width, though rarely covered wholly with water—great insular masses challenge astonishment, by the rate at which they are being carried bodily off in winter.

One of the more remarkable of these is seen in Sketch No. 258: they all consist of great beds of calcareous breccia, resting conformably upon perfectly level deep beds of extreme thinness of parallel lamination of green, grey, and purple clays, or marls, hard, dense, and unctuous, but rapidly softened and dissolved when wetted. Above the breccia, lies an immense thickness of dense red brown, clay and loam; the laminated marl beds exist, just at the level of the watercourse of the two rivers, and as these get rapidly sapped and cut away, huge masses of the breccia, break off and fall separate into small pieces, and with the clays shed off their summits, are swept away, leaving nothing deposited finally upon the river-beds, but the harder calcareous pebbles and boulders of the breccia, and those still harder travelled boulders, which it contained in abundance. Amongst the latter, are many of sienite and yellow granites, some of a green and white fine sandstone breccia, having lithologically a most suspicious look of indurated chalk, from a green sand formation, and many of variegated jaspers. Large blocks of the latter, banded with green and purple, are found abundantly in the clays and on the slopes to the north side