and in conjuring up visions of earthquakes, and frightful abysses from which there ever rose a lurid glare as hill after hill of molten rock came belching up from the fires below. But while far from denying that such appearances may have been sometimes seen during the long lapse of the geological ages, and that they give no little vividness and sublimity to a geological picture, we claim for the doctrine of the tranquil and uniform operation during past time of existing laws and forces, an element not less poetic. In the former case the pervading idea is that of unlimited expenditure of power, in the latter that of unlimited lapse of time. In the one case the action is Titanic but transient, in the other it is tranquil but immensely protracted. The two doctrines in this way counterbalance each other; yet I cannot but think that however impressive it may be to stand in some lone glen, and while gazing at its dark jagged precipitous cliffs, to dream about the paroxysmal convulsions of some hour far back in the distant past, the scene becomes yet more impressive when we look on its nakedness and sublimity not as the sudden and capricious creation of a day, but as the gradual result of a thousand centuries. These cliffs may once have been low-browed rocks rising but a little way out of a broad grassy plain, and serving as a noon-tide haunt for animals of long extinct races. Thousands of years pass away and we see these same rocks higher and steeper in their outline, brown with algæ and ever wet with surf, while around them stretches a shoreless sea. Ages again roll on, and we mark still the same rocks shooting up as bleak crags covered with ice and snow. Another interval of untold extent elapses, and rock, snow, and ice have all disappeared beneath a broad ocean cumbered with ice-floes and wandering bergs. Again the curtain drops upon the scene, and when once more it rises, the cliffs stand out in much the same abrupt precipitous aspect with that which they now present, save that their bald foreheads look less seamed and scarred than now, and their dark sides show no trace of bush or tree. The white cascades that to-day pour down from their summits and sides--seeming in the distance like the white hairs of age--are insensibly deepening the scars and furrows on these ancient hills, and thus slowly but yet surely carrying on the process of degradation and decay. Musing on all this long series of stages in the formation of one single cliff-line, is there not something more sublime, something yet more impressive than if we pictured but the chance random result of the gigantic paroxysm of an hour? Let us not be deterred then from seeking an explanation of the origin of the ravine among some of the quieter and more unobtrusive forces of Nature. Give them but an unlimited period to work in and they will abundantly satisfy all our demands.