We find figured by M'Culloch, in his "Western Islands," the internal cavity of a pebble of Scuir More, which he picked up on the beach below, and which had been formed evidently within one of the larger vesicles of the amygdaloid. He describes it as curiously illustrative of a various chemistry; the outer crust is composed of a pale-zoned agate, inclosing a cavity, from the upper side of which there depends a group of chalcedonic stalactites, some of them, as in ancient spar caves, reaching to the floor; and bearing on its under side a large crystal of carbonate of lime, that the longer stalactites pass through. In the vesicle in which this hollow pebble was formed three consecutive processes must have gone on. First, a process of infiltration coated the interior all around with layer after layer, now of one mineral substance, now of another, as a plasterer coats over the sides and ceiling of a room with successive layers of lime, putty, and stucco; and had this process gone on, the whole cell would have been filled with a pale-zoned agate. But it ceased, and a new process began. A chalcedonic infiltration gradually entered from above; and, instead of coating over the walls, roof, and floor, it hardened into a group of spear-like stalactites, that lengthened by slow degrees, till some of them had traversed the entire cavity from top to bottom. And then this second process ceased like the first, and a third commenced. An infiltration of lime took place; and the minute calcareous molecules, under the influence of the law of crystallization, built themselves up on the floor into a large smooth-sided rhomb, resembling a closed sarcophagus resting in the middle of some Egyptian cemetery. And then, the limestone crystal completed, there ensued no after change. As shown by some other specimens, however, there was a yet farther process: a pure quartzose deposition took place, that coated not a few of the calcareous rhombs with sprigs of rock-crystal. I found in the Scuir More several cellular agates in which similar processes had gone on,--none of them quite so fine, however, as the one figured by M'Culloch; but there seemed no lack of evidence regarding the strange and multifarious chemistry that had been carried on in the vesicular cavities of this mountain, as in the retorts of some vast laboratory. Here was a vesicle filled with green earth,--there a vesicle filled with calcareous spar,--yonder a vesicle crusted round on a thin chalcedonic shell with rock-crystal,--in one cavity an agate had been elaborated, in another a heliotrope, in a third a milk-white chalcedony, in a fourth a jasper. On what principle, and under what direction, have results so various taken place in vesicles of the same rock, that in many instances occur scarce half an inch apart? Why, for instance, should that vesicle have elaborated only green earth, and the vesicle separated from it by a partition barely a line in