Sec. 1. It will be remembered that we resolved to give generally the term "coherent" to those rocks which appeared to be composed of one compact substance, not of several materials. But, as in all the arrangements of Nature we find that her several classes pass into each other by imperceptible gradations, and that there is no ruling of red lines between one and the other, we need not suppose that we shall find any plainly distinguishable limit between the crystalline and coherent rocks. Sometimes, indeed, a very distinctly marked crystalline will be joined by a coherent rock so sharply and neatly that it is possible to break off specimens, no larger than a walnut, containing portions of each; but far more frequently the transition from one to the other is effected gradually; or, if not, there exist, at any rate, in other places intervening, a series of rocks which possess an imperfectly crystalline character, passing down into that of simple coherence. This transition is usually effected through the different kinds of slate; the slaty crystallines becoming more and more fine in texture, until at last they appear composed of nothing but very fine mica or chlorite; and this mass of micaceous substance becomes more and more compact and silky in texture, losing its magnesia, and containing more of the earth which forms the substance of clay, until at last it assumes the familiar appearance of roofing-slate, the noblest example of the coherent rocks. I call it the noblest, as being the nearest to the crystallines, and possessing much in common with them. Connected with this well-known substance are enormous masses of other rocks, more or less resembling it in character, of which the following are universal characteristics. Characteristics of Slaty Coherents. 1. Softness of texture. 2. Lamination of structure.