The secondary or floetz-limestone contains several formations that resemble each other very much, and differ principally by the newer being more earthy than the older. To these succeed, as we have already men tioned, chalk and calc-tuff, which are in general still more earthy in their external appearance.
It is not enough, Werner continues, to detail the dif ferences and agreements of this great series ; we must also endeavour to discover how these have been pro duced. The whole series, as has been already observ ed, is completely chemical, yet the different members have distinct characters of difference. In the first and second periods, the productions are almost entirely che mical, but the crystallization becomes more imperfect, the newer the formation. Lastly, in the third period, the members of the series become mixed with small portions of mechanical matter, as is shown by the earthy aspect of many fleetz-limestones. We know the condi tions necessary for the formation of a crystalline struc ture, and that rest and motion are the agents which assist or prevent its regular formation. Hence we may fairly infer, that the solution, or ocean, when it stood high over the earth, was calm and undisturbed. During succeed ing periods, the solution appears to have become more and more agitated; yet at first it only prevented the per fection of the crystallization. As the water diminished in height, its motions increased ; its destroying powers reached to the surface of the earth, and the crystalline shoots were destroyed, and thus the first mechanical productions were formed. The water still continuing to diminish, the dry land began to appear ; of course the mechanical action of the water woule: be much increased, as also the formation of mechanical productions. How admirably does this agree with the appearances present ed by this series of formations ! The connection and import of all thesa appearances will be more apparent, if we take a view of the charac teristic position of the strata in the different members of this series of formations, and of their relations to the exterior of the earth. This will be considered particu larly afterwards. At present we shall only mention the highly elevated level of the limestone in gneiss, con trasted with the low situation of chalk and calc-tuff.
2. Slate Formation-Suite.
This is a very extensive series of formations.* The limestone series is composed only of limestone, and a single earth, as its principal constituent part. In the series of clay-slate formations, on the contrary, different earths have united together, to form the rocks we shall now mention. Silica, alumina, and magnesia, but par ticularly the two latter, are the most characteristic earths belonging to this suite of formations. We shall begin the description with that member of the series which may be considered as a central point from which the others diverge, and which gives the name to the whole series. This is clay-slate. It is evident, that the oldest clay-slate must border on the newest Mica slate ; and the newest, on transition-slate. The oldest clay-slate has more lustre than the newer, and is even slightly micaceous, so that it resembles the fine slaty mica slate OD which it rests. The newer clay-slate has a darker grey colour, less lustre, and contains finely disseminated scales of mica, which brings it nearer to the transition-slate. Mica-slate is an aggregate rock, composed of quartz and mica : but in the older, it be comes gradually intermixed with felspar, which, in the oldest varieties, increases, and shows itself more and more as an essential constituent part, until the mica slate passes into gneiss. The texture of the newest gneiss which lies nearest to mica-slate is still thin slaty ; but it becomes gradually coarser, more crystalline, thick slaty, and very nearly granular, when it passes into granite. In granite, the texture is completely granular, and this rock stands as the first and oldest member of the series.
The same clue will conduct us back to the transi tion-slate, which occurs in mountains of grey-wacke. Here distinct mechanical matter is mixed with the chemical. Grey-wacke is a complete sandstone ; we have a gradation of its grains from those the size of a pebble, until, from their smallness, they are no longer distinguishable ; and this constitutes a transition to grey wacke-slate.