If nature be the model for art in the composition of landscape, we must imitate her process as well as her effects: water, by its own power of gravitation, seeks the lowest ground, and runs along the valleys.* If, in its course, the water meets with any obstruction, it spreads itself into a lake, or meer, proportionate to the magnitude of the obstruction; and thus we often see, in the most picturesque counties, a series of pools connected by channels of the rivers which supply them. *[Indeed, I have sometimes fancied, that, as action and re-action are alike, and as cause and effect often change their situations, so valleys are increased in depth by the course of waters perpetually passing along them: thus, if the water only displaces one inch of soil in each year, it will amount to five hundred feet in six thousand years, and this is equal to the deepest valleys. In loose soils, the sides of the hills will gradually wash down, and form open valleys; in hard soils, they will become narrow valleys: but ravines I suppose to be the effect of sudden convulsions from fire or steam, and not made by any gradual abrasion of the surface.]
