Page:A Treatise on Geology, volume 2.djvu/338

 324 strata. And as among these the materials present unequal resistance to the atmospheric agents of destruction, and waste unequally, long chains of limestone hills alternate with wide parallel vales of clay, and render a journey from London to Bath, Worcester, or Newark, a succession of similar vales and hills. One tertiary vale, one cretaceous ridge, one or more vales in clay, alternating with as many ridges of oolite, are crossed on each of these roads in the same order of succession. These parallel vales are frequently, though not always, filled for parts of their length by great rivers, like the Isis or the Thames; and investigation easily shows that the hollows are not the result of fluviatile action, but of some earlier and greater force of nature, which excavated the wide vale in which the river now finds a narrow channel. There can be little room for doubt that the currents and tides of the sea, in action at the time of the elevation of the land from its ancient level, were the instruments by which the softer strata were worn away, and thus, with a considerable approach to accuracy, we may assert, in general terms, that by direct and indirect effects, the leading features of the earthy surface are distinctly referrible to the force of interior heat.

The charm of rural landscapes, the romantic pleasure of mountain prospects, and sequestered dells and waterfalls, is but feebly appreciated by those who, unacquainted with the principles of art, have not learned to perceive in all the works of nature the operation of law, and to trace in all the diurnal aspect of creation the effect of many preceding revolutions. The greater features of physical geography are explained by subterranean movements and their consequences; the minuter proportions, which are the proper province of pictorial art, are partly due to other circumstances. The richness or desolation of countries, besides the obvious influence of elevation and climate, proximity to the sea, or snowy mountains,