down to complete opacity. The shades are arranged in globular concentric folds around a central nucleus, or in a wavy strata—the differently-shaded layers arranging themselves in accordance with the sinuosi ties of the adjoining layers. The mass is made up of fine globules, which often show a radio-concentric structure ; and in most cases has been formed from a cupriferous solution which has successively deposited its residue in a stalagmitic form. 1 Concretionary mala chite occurs in mammilated masses of undulating parallel beds, striated in the direction of their thick ness, the surfaces of contact being often overspread with pulverulent malachite, or decorated with black dendrites, which have a very pretty effect on the greenish ground. The masses are rarely homogeneous and compact, often containing cavities which render the mineral unfit for ornamental use; but large masses free from such defects have occasionally been procured: one piece, especially cited, having been fashioned into a table eighty-five centimetres long, and forty-five broad. 2 The largest masses of this ore of copper have been obtained from the Ural mountains; one of which is described by Murchison, and his companions in travel, as having been found at Nijni Tagilsk, occupy ing a fissure between schaalstein on the one side, and 1 Murchison, Geol. of Russia, i. p. 374. 2 Brongniart, Traits de Min. ii. 223.