The facts we have just detailed lead us to distinguish two grand epochas in the formation of rocks ; the first anterior, and the second posterior, to the formation of organic beings. The rocks of the first division are named (primitive; they contain no fossil organic remains, are situated below the others, and are wholly of chemical formation. The rocks posterior to the creation of orga nized beings are denominated secondary. Several of these resemble those of the primitive class in composi tion and structure ; but differ from them in containing petrifactions. These Werner denominated transition, and other geologists, intermediate. They partake partly of the primitive, partly of the secondary character, hence are named intermediate or transition. These transition rocks become intermixed with sandstones, and other rocks of the same description, and at length disappear; when a series of sandstone and limestone rucks, remark able for their abundance of vegetable and animal re mains, make their appearance, and form the secondary, or fatz rocks of geologists. The newer, or upper rocks of the secondary class, are covered with an alternating series of limestone, gypsum, clay, sandstone, and sand, which abounds in fossil organic remains, and particularly of quadrupeds. The name tertiary has been given to these.
The great beds of gravel, sand, clay, marl, &c. which rest on the rocks of the preceding classes, form a class named alluvial. They contain abundance of organic re mains, and even of animals, at the top of the zoological scale. Those rocks, which are undoubted productions of fire, are named volcanic, and form the fifth and last class of the series of mountain locks. They arc often posterior to secondary rocks, and sometimes even to substances of the alluvial class.
Werner, as indeed appears from what has been al featly stated, seems to consider all the mineral forma tions as formed by one and the same solution, which has gradually changed in height and in nature. But he saw that this explanation would not apply to every case: for example, if every rock, or bed, should occur at a height corresponding to its age, that is, at a higher level in old than in new rocks, how does it happen that porphyry, re sembling those in primitive regions, rests upon secon dary rocks, and attains a great elevation ? A simple oscillatory movement, Werner remarks, would not ex plain this arrangement. It follows, therefore, according to Werner's principles, that a new solution must have invaded the district already abandoned by the old solu tion, and deposited the newer formations. Werner admitted these new inundations, and attributed to them some particular formations, such as the secondary trap rocks, and ceitain primitive porphyries.
Werner remarks, that when we view the various de positions from the earliest discoverable period to the newest, we find in them such differences, as show that the contents of the water of the globe must have chang ed by degrees, and that all its depositions form beautiful and connected series. The oldest rocks, which are pure chemical precipitates, arc composed principally of silice ous, argillaceous, and magnesian earths. The rocks, as granite, gneiss, and mica-slate, contain metals that are of cotemporaneous formation with them, and that scarce ly occur in newer periods ; these are tin, molybdena, and tungsten.
This state of the water of the globe, however, alters gradually and remarkably, as we approach the newer periods, by the appearance of limestone in quantity, coal, and salt, and the disappearance of old and the appear ance of new metals. Besides this general succession, (which will afterwards he particularly considered,) dis coverable in the productions of different periods, we have instances of the repetition of certain products at considerable intervals, and in formations of different arras and kinds. In a series of this kind, all the mem bers have general characters of agreement, and the in dividual members bear characters expressive, not only of the period of their formation, but also of the circum stances under which they were formed. Such a series,
as we hare already mentioned, is denominated a Principal Formation Szite, or Series of Formations. By contrast ing the old and new members of such a series, the dif ference will be found so great, that we can with difficulty recognize them as members of the same formation suite: on the contrary, the immediately preceding or following members are so much alike, that it is equally difficult to distinguish the one from the other. This shews how much the prevailing circumstances that existed during the time of their formation, were alike in the members of the same age, and differed in those of a dif ferent date.
We shall now illustrate this subject by a short ab stract of Werner's descriptions of several of these series of formations.
1. Limestone Formation-Suite.
The first member of this series is the white granular limestone, which occurs in primitive rocks, as gneiss, mica-slate, and clay slate. This limestone has large granular distinct concretions ; but in the newest clay slate, the concretions become more minute, and it even approaches to compact. The transition rocks contain the second member of this series, the variegated lime stone, which has less translucidity than the preceding, but more than the following members of the series, and shews the first traces of petrifactions. The following, or flcetz locks, contain the third member of the series, the grey ficetz-limestone, which is scarcely translucent on the edges, and is full of petrifactions. It has some resemblance to the limestone of the transition period, but only a very remote one to that of the primitive. How great is the difference between the granular translucent primitive limestone, and the dull earthy and nearly opaque flcetz limestone ; and yet both are members of a series of chemical formations, which are still not the most distant. Chalk is a still newer formation, and the limestone and marls of the Paris formation connect the foregoing members, which have been deposited from the ocean, with the calc-tufl; the lowest link of this series of formations, (if we do not include the coral-rocks that arc daily forming) which has been formed on the land. We have thus a complete series from the earliest to the latest period, in which we observe a gradual disappear ance of the crystalline, and increase of the earthy aspect, corresponding with the relative age of the different mem bers of the series, and the state of the solvent from which they were precipitated, and all serving as proofs of the immensely great, but gradual alteration of the state of the universal waters. If we even examine the individual members of this series, we find these gradations still more minute, hut always very characteristic. Thus the limestone of the primitive period, (that which occurs in gneiss,) has the largest granular distinct concretions, and possesses the highest degree of translucidity and lustre, and has therefore the most highly crystalline structure of the whole series. Does not the highly crys talline structure correspond most intimately with a calm state of the solution? The next member of the series, which is still crystalline, but with smaller distinct con cretions, nccurs in mica-slate ; and, still less crystalline, or with smaller distinct concretions, in the oldest clay slate. In the newer clay-slate, on the contrary, the dis tinct concretions are so small, as only to be discoverable by their glimmering and translucidity. The white co lour, which hitherto characterised the older limestone, is now intermixed with black, red, &c ; and the newest members of this formation form the transition to the products of the next period. In the transition period, the limestone is compact, translucent, glimmering, and variegated or marbled.