associations; appearing to be peculiarly attached to no rock, whereas there is a predominant, though ndt a constant, affinity and order, among many others of the primary strata. It is almost unnecessary to say, that it presents many varieties of texture, from the large crystalline to the most minute saccharine grain, and from a smooth and flat conchoidal fracture, to one of an earthy and dull aspect. It often differs from the secondary, in containing various imbedded minerals; though not so often as to form a sure ground of distinction. These will be found enumerated in the Classification of Rocks: while their existence proves, demonstrably, that the strata in question have been fused; giving occasion as in micaceous schist, to the crystallization of similar igneous minerals. Its well-known chemical properties render a definition superfluous: but the student must recollect, that the indurated kinds do not readily ef fervesce unless previously powdered. If it is superfluous to mention its oeconomical uses, yet, as it often contains alternating laminae of other roeks, so as not to burn readily into lime, it is often neglected, even when fit for all the purposes of ma sonry or agriculture. Being a limited rock, it is not very productive of metallic veins ; but it is said that lead, manganese, silver, zinc, and gold, have been found in it. How widely it is used as marble, I need not say; while its ornamental varieties are amply recorded.