5. The normal position of terrestrial or stony beds producing aqueous deposits is horizontal. When one sees these immense plains, often extending as far as the eye can see in a perfectly horizontal line, united as if leveled by a roller, or depths of valleys as smooth as the surface of a lake, one can be certain that at some distant epoch these places have been for a long time covered by tranquil waters, which, in retiring, have left the beds dry upon which they were deposited during their sojourn. After the retreats of the waters, these beds have become covered with vegetation. If in place of fertile, muddy clay or chalky ground, which afford nourishment for soil, the waters had deposited only siliceous sand without aggregation, we should find here dry and sandy plains constituting waste lands and deserts. The deposits left by partial inundation and those which form the alluvium at the mouth of rivers, give us a faint idea of this.