Sec. 20. The quantity of admissible transgression of law varies with the degree in which the ornamentation involves or admits imitation of nature. Thus, if these ivy leaves in Fig. 99 were completely drawn in light and shade, they would not be properly connected with the more or less regular sequences of the scroll; and in every subordinate ornament, something like complete symmetry may be admitted, as in bead mouldings, chequerings, &c. Also, the ways in which the transgression may be granted vary infinitely; in the finest compositions it is perpetual, and yet so balanced and atoned for as always to bring about more beauty than if there had been no transgression. In a truly fine mountain or organic line, if it is looked at in detail, no one would believe in its being a continuous curve, or being subjected to any fixed law. It seems broken, and bending a thousand ways; perfectly free and wild, and yielding to every impulse. But, after following with the eye three or four of its impulses, we shall begin to trace some strange order among them; every added movement will make the ruling intent clearer; and when the whole life of the line is revealed at last, it will be found to have been, throughout, as obedient to the true law of its course as the stars in their orbits. [Illustration: FIG. 99.] The four systems of mountain line. Sec. 21. Thus much may suffice for our immediate purpose respecting beautiful lines in general. We have now to consider the particular groups of them belonging to mountains. The lines which are produced by course of time upon hill contours are mainly divisible into four systems. 1. Lines of Fall. Those which are wrought out on the solid mass by the fall of water or of stones. 2. Lines of Projection. Those which are produced in debris by the bounding of the masses, under the influence of their falling force. 3. Lines of Escape. Those which are produced by the spreading of debris from a given point over surfaces of varied shape. 4. Lines of Rest. Those which are assumed by debris when in a state of comparative permanence and stability. 1. Lines of Fall. 1. Lines of Fall. Produced by falling bodies upon hill-surfaces. However little the reader may be acquainted with hills, I believe that, almost instinctively, he will perceive that the form supposed to belong to a wooded promontory at _a_, Fig. 100, is an impossible one; and that the form at _b_ is not only a possible but probable one. The lines are equally formal in both. But in _a_, the curve is a portion of a circle, meeting a level line: in _b_ it is an infinite line, getting less and less steep as it ascends. [Illustration: FIG. 100.]