Pit-coal and common salt, and almost all the metals, likewise occur in veins. Some veins are filled with water-worn pebbles, as one observed by Werner at Joachimstahl*. Some are filled with loam t. Nay, they even sometimes contain petrifactions. Thus the Baron de Born describes a petrified popites which he saw in a compact cinnabar vein in Hungary; and Mr. de Schlottheim communi. cated an account of a still more remarkable appearance of the same kind to Werner. In a calcareous mountain in Thuringia, there occur veins of marl five or six inches.thick, containing petrifactions differing altogether from those which are found in the lime-stone. The petrifactions found in the marl are, cornua ammonis, terebrates, and turbinites; while those that occur in the lime-stone rock are trochites. Beds of the marl occur in the neighbourhood; and these beds contain the same petrifactions that are found in the veins t. 3. It is very common to find veins crossing each other in the same rock. When that happens, one of the veius may be traced passing through the other without any interruption, and cutting in two, while the other always separates, and disappears at the point of crossing. 4. Such is a short sketch of the most remarkable phænomena respecting veins. Werner supposes that they were originally fissures formed in the rocks, and that they were all gradually filled by minerals depositsd slowly from above, while the rocks in which they occur were covered by water, and that they were filled at the same time that the different formations were deposited. This theory he has supported in his book on Veins, by a very complete enumeration of all the circumstances respecting their structure and appearances. He has shown that they resemble fissures very exactly in their shape and direction; and that as they contain petrifactions and minerals altered by the action of water, they must of necessity have been filled from above. Veins of course, according to this theory, are newer than the rocks in which they occur; and when two veins cross, that is obviously the newest which traverses the other without interruption, as the fissures constituting the second vein must have been formed after → Werner, Nouvelle Theorie, p. 81. Ibid. p. 88. The aggregated rocks are likewise of two kinds; namely, I. Indeterminate. Only one instance of this kind of aggregation has hitherto occurred, namely in the older serpentine, where limestone and serpentine are so conjoined, that it is difficult to say which predominates. II. Determinate. The determinate are either, I. Single aggregated; or, II. Double aggregated. There are four kinds of single aggregated rocks; namely, 1. Granular; composed of grains whose length, breadth, and thickness are nearly alike, and which are of contemporaneous for. mation. As granite, sienite. 2. Slaty; composed of plates laid above each other; as mica slate. 3. Porphyritic; composed of a compact ground, containing in it crystals which appear to have been deposited at the time the rock was formed; as common porphyry. 4. Amygdaloidal; composed of a compact ground, containing in it vesicles which appear to have been afterwards filled up; as amygdaloid. There are five kinds of double aggregated rocks; namely, 1. Granular slaty; composed of slaty masses laid on each other. Every individual slate is composed of grains cohering together; or it is slaty in the great, and granular in the small; a gneiss. 2. Slaty granular; composed of large granular masses cohering together; each grain is composed of plates; or the rock is granular in the great, and slaty in the small; as topaz rock. 3. Granular porphyritic; granular in the small, and porphyritic in the great; as granite, greenstone frequently. 4. Slaty porphyritic; slaty in the small, porphyritic in the great; as mica slate frequently. 5. Porphyritic and amygdaloidal; a inass porphyritic and amygdaloidal at the same time; as amygdaloid and basalt frequently. Such are the different kinds of structures of rocks hitherto observed and described. The following Table will give the reader a synoptical view of these different kinds of structure: 1. Simple rocks II. Compound rocks A. Çemented B. Aggregated a. Indeterminate b. Determinate I. Single 1. Granular 2. Slaty 3. Porphyritic 1. Granular slaty 2. Slaty granular 3. Granular porphyritic 4. Slaty porphyritic 5. Porphyritic and amygdaloidal SECT. II. Of the relative Situation of Rocks. The rocky masses, or rocks, hitherto observed, amount to about sixty. Of these rocks, variously placed over each other, the whole crust of the earth is composed, to the greatest depth that the industry of man has been able to penetrate; and with respect to each other, they occupy for the most part a determinate situation, which holds invariably in every part of the earth. Thus lime-stone is no where found under granite, but always above it. Were we to suppose every particular rock, or layer, which constitutes a part of the earth's surface to be extended round the whole earth, and to be wrapped round the central nucleus, like the coat of an onion, in that case every rock would be constantly found; one species would be always lowest or nearest the centre; another species would uniformly rest upon this first; a third upon the second, and so on. Now, though the rocks do not in reality extend round the earth in this uninterrupted manner; though, partly from the inequality of the nucleus on which they rest, partly from their own inequality of thickness in different places, and partly from other causes, the continuity is often interrupted; yet still we can trace enough of it to convince us that the rocks which constitute the earth's crust, considered in a great scale, are every where the same, and that they invariably occupy the same situation with respect to each other. Werner has therefore chosen this relative situation as the basis of his classification of rocks. He divides them into five VOL. I. Y classes. The first class consists of those rocks which, if we were to suppose each layer to be extended over the whole earth, would in that case lie lowest, or nearest the centre of all the rocks which we know to be covered by all the other rocks. The second class consists of those rocks which in that case would be immediately above the first class and cover them. The third class would cover the se cond in the same manner; the fourth the third; and the fifth would be uppermost of all, and constitute the immediate surface of the earth. The first class of rocks are covered by all the rest, but never themselves lie over any other. The others lie in order over each other. These grand classes of rocks he has denominated for. mations, and distinguished them by the following specific names: I. Primitive formations II. Transition formations III. Floetz, or horizontal formations V. Volcanic The primitive formations are of course the lowest of all, and the alluvial constitute the very surface of the earth; for the volcanic, as is obvious, are confined to particular points. Not that the primitive are always at a great depth under the surface, very often they are at the surface, or even constitute mountains. In such cases, the other classes of formations are wanting altogether. In like manner the transition, and other formations, may each in its turn occupy the surface, or constitute the mass of a mountain. In such cases, all the subsequent formations which ought to cover them are wanting in that particular spot. Each of these grand classes of formations consists of a greater or smaller number of rocks, which occupy a determinate position with respect to each other, and which, like the great formations themselves, may often be wanting in particular places. Let us take a view of the rocks which compose all these different formations. Class I. Primitive Formations. The rocks which constitute the primitive formations are very numerous. They have been divided therefore into seven sets, which constitute as many primitive formations, and are distinguished each by the name of that particular |