Page:Popular Science Monthly Volume 33.djvu/551

Rh often resembling mountains, which for the most part follow the trend of the steppe, as well as the direction of the prevailing wind, which is here from southeast to northwest. The hills rise, counting from the nearest valleys, to a height of fifty-five metres, inclining gently on the windward side, but presenting a steep slope on the lee. This steppe has indeed always in historical times included bare spaces, varying in number and extent according to the existing state of cultivation. Till the beginning of the present century the bare drift-sand had so gained the upper hand that there was in the middle of the tract a continuous extent of one hundred and fifty square kilometres in which grass and shrub land could be found only in small spots and streaks. Only the northeastern and southeastern part of the steppe consisted of grass-land, in which bare spaces were likewise not wanting. Many other such sand-districts might be named. For example, there were in the County Pesth, in 1809, nearly 1,600 square kilometres of more or less bare, but not continuous sands.

Let us inquire into the origin of these sand-masses. The open sea is usually bordered by deposits of sand and gravel. Where the shore rises in steep rocks, these deposits are concealed under the water; but where the coast is alluvial, as is generally the case in the smaller seas, the whole shore consists of sand and shingle; and the sea-drift extends up upon the dry land. The waves are constantly bringing up new material to the beach, chiefly consisting of fine sand. A storm stirs the water to a considerable depth, pushes the sand forward, and bears it with the waves high upon the shore. On the retreat of the waves, a part of the sand remains, because it is specifically lighter than water. When the storm has subsided, and the sea has withdrawn to its proper limits, the sand becomes dried, and falls under the power of the strong, restless wind, which takes up all the fine particles, and when it rises to be a storm wind some of the coarser ones too, and carries them away into the country. Here it meets impediments of various forms and efficiency; then it drops its load irregularly, and gradually piles up along the shore those hills which are generally known as sea-coast dunes.

This edging of dunes which borders the flat sea-shore is of various breadths in different places. In some places it becomes so piled up as to cause a retreat of the waves. New dunes are constantly formed farther toward the sea, and the dune-zone is widened. Sometimes the widening is effected by the emigration of the bare dunes toward the interior. In other places the dunes are broken into by the sea-water, and suffer loss of breadth.

When there is no overflowing of the shore or breaking up of the dunes, the system usually consists of three more or less connected rows of hills. First, the fore-dunes, which first receive the