It was for a long time supposed, that the chains of the high mountains run from west to east, till the contrary was found in America. But no person before M. Bourguet discovered the surprising regularity of the structure of those great masses: he found (after having crossed the Alps thirty times in fourteen different parts of it, twice over the Apennine mountains, and made divers tours in the environs of these mountains, and of Mount Jura) that all mountains are formed nearly after the manner of works of a fortification. When the body of the mountain runs from east to west, it forms prominences, which face the north and south; this wonderful regularity is so striking in vallies, that we seem to walk in a very regular covered way; if, for example, we travel in a valley from north to south, we perceive that the mountain on the right forms projections which front the east, and those of the mountain on the left front the west, so that the saliant angles of one side reciprocally answer the returning angles of the other, which are always alternatively opposed to them. The angles which mountains form in great vallies are less acute, because the direction is less steep, and they are farther distant from each other. In plains they are not so perceptible, except by the banks of rivers, which are generally in the middle of them, and whose natural windings answer the most advanced angles or striking projections of the mountains. It is astonishing so visible a thing was so long unobserved, for when in a valley the inclination of one of the mountains which border it is less steep than that of the other, the river takes its course much nearer the steepest mountain, and does not flow through its middle.