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157 CHAP, xxvir. Micaceous Schist. Chlorite Schist. Talcose Schist. Though I have placed Micaceous schist next to gneiss, in conformity to the general opinions respecting its order in nature, it has already appeared, and will soon be still more evident, that this order is not constant. If a definition of so familiar a rock is nearly super fluous, it is needful to say, that it ranges between mica and quartz, so that as the examples on one side consist of little else than condensed mica, the others pass into quartz rock by an imperceptible gradation; as is com mon especially at the mutual boundaries of these two deposits. The varieties must be sought in the Clas sification of Rocks; yet I must note here, as essential to its theory, that it occasionally contains fragments, or portions of a conglomerate. In this island, micaceous schist is limited to moun tainous districts; the features which it confers on the country being various, and often picturesque. In some tracts, the hills are tame and undulating, like those of argillaceous schist; ranging from 500 to 1000 feet in height, and rarely broken by projecting rocks, whence they gradually rise to upwards of 4000 as in Ben Lawers; acquiring more striking characters, and displaying abrupt precipices, with summits occasion ally serrated, and partially covered with vegetation. As this rock often presents considerable fissures, and, while mouldering more readily than gneiss, is favour able to vegetation, the lower cliffs and precipices are often covered with trees, producing a variety of pic turesque scenery well known in the vicinity of Loch Cateran. In Scotland, as elsewhere, it occupies ex tensive tracts, unmixed with any other rock, but oc-