2. Strata can only be formed by parallel seams, which have the same direction and extent through the moun tain-mass. Where parallel rents occur in different di rections in the same species of rock, as in granite, sand stone, lime-stone, Ste. it is evident that they arc to be considered as accidental.
3. The seams of tabular distinct concretions, which are often of considerable extent, should not be confound ed with strata seams, because their extent is not so con siderable ; and in each group of concretions the direction is different.
4. Where parallel rents have a different direction from the slaty structure of the stone, they are certainly accidental. Inattention to this circumstance has led mineralogists into error. I observed a striking instance of these rents it) a quarry of gneiss, in the forest of Tharand, in Upper Saxony. The gneiss, at first sight, appeared to be disposed in vertical strata, and as such it was viewed by De Luc : on a closer examination, how ever, the apparent vertical seams proved to be merely accidental parallel rents, perpendicular to the slaty structure of the stone; therefore the strata were hori zontal, not vertical.
5. Beds are generally parallel with the strata ; these, therefore, point out the direction of the strata.
6. Although the slaty structure points out to us the direction which the strata must have, it does not follow, that a rock having a slaty structure is stratified.
7. In sand-stone, lime-stone, and rock-salt, regular and very extensive stripes are sometimes observed, which have been confounded with true seams of stratification. An attentive examination, however, always discovers them traversing the real strata seams. Von Buch, in his description of Landeck, and geognostical observa tions made in Italy and Germany ; and Friesleben, in his observations on Thuringia, describes striking instances of stripes resembling strata-seams.
Strata vary very considerably in the angle which they form with the horizon ; they occur from horizontal to vertical, but the general inclination is between horizontal and The differences are either original, or have been produced by subsequent changes.
Certain species of rock are constantly stratified, while others either are not stratified, or only in an imperfect manlier. All the secondary rocks, such as lime-stone, sand-stone, coal, &c. are very distinctly stratified. In the
most modern of the secondary rocks, the strata arc often horizontal, and frequently extend to a great distance of the same thickness. In more ancient rocks of this class, as in certain lime-stones and in gypsum, the stratification is less distinct, and the position of the strata is not so horizontal. In the coal formation, which is of a still older date, the stratification is very distinct, but the beds are frequently variously waved and convoluted, and often highly inclined. In the transition and primitive classes, many rocks, such as gneiss, and clay-slate.
are distinctly stratified, while others, as granite, porphyry, trap, limestone, gypsum, serpentine, and quartz, are in general but imperlectly stratified, and the strata of these two classes more often incline to the vertical than to the horizontal position.
Rocks which appear to have been mere deposites or mud, gravel, sand, &c. have been formed by successive depositions, while others, such as gypsum, limestone, quartz, gneiss, mica-slate, clay-slate, granite, &c. owe their stratified structure to crystallization, from a more or less perfect state of solution. This latter opinion is illustrated by the uninterrupted transitions of the beds into each other, and by the position of the embedded crystals and masses to the surrounding rock.
On examining the structure of a mountain or tract of country, we must be careful to avoid all unnecessary minuteness, otherwise we shall fail in acquiring a dis tinct conception of it. This observation is founded on a knowledge of the geognostical features of nature, which are all on the great scale.
By not attending to this mode of examination, geolo gists have fallen into errors, and given to extensive tracts of country a most irregular and confused structure. Speculators, building on these errors, have represented the whole crust of the globe as an irregular and unseem ly mass. It is indeed surprising, that men possessed of any knowledge of the beautiful harmony that prevails in the structure of organic beings, could for a moment be• lieve it possible, that the great fabric of the globe itself, —that magnificent display of Omnipotence,—should be destitute of all regularity in its structure, and be nothing more than a heap of ruins.