Page:An Introduction to the Survey of Western Palestine.djvu/23

7 THE SURVEY OF WESTERN PALESTINE

INTKODUCTION.

To appreciate the use and value of the New Survey, it is necessary to examine it in some detail, and to bring it into comparison with the information that existed previously. Passing over the methods by which a survey is accurately made, it is enough at present to observe that the foundation of a geographical map is its Outline, consisting chiefly of the delineation of its Waterways. A distinct acquaintance with this branch of the subject is a fundamental element of geographical knowledge.

To describe the waterways of a country intelligibly, it is needful to adopt a simple method, based on the following facts. In tracing a watercourse from its source to its final outfall, it is found that some outfalls dispose of the waters of very small areas with simple systems of watercourses ; while other outfalls are the drains of very large areas, with a great complication of watercourses, not easily unravelled. The area drained through each distinct outfall or mouth, is called a Basin, whether it be small or large ; and its boundary is a Waterparting. The surfaces descending from a Waterparting to a Watercourse are called Watersheds or Slopes. The term Watershed or Slope is equally applicable to the sides of the smallest valley or of the largest continent. In the latter case, the term includes all the basins into which the same continental slope is divided. In like manner a Waterparting may be a simple ridge or mere swelling of the ground between

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