The area included in the Philadelphia district lies between 39° 45' and 40° 15' north latitude and 75° and 75° 30' west longitude. It has a length of 34.50 miles from north to south and a width of 26.53 miles from east to west, and covers one-fourth of a square degree, which is equivalent, in that latitude, to, about 915.25 square miles. It is mapped on the Germantown, Norristown, Philadelphia, and Chester atlas sheets of the United States Geological Survey. a Each of these sheets represents a tract fifteen minutes in extent each way. This district is in Pennsylyania, New Jersey, and Delaware, and comprises, in whole or in part, ten counties-Bucks, Montgomery, Philadelphia, Delaware, and Chester counties in Pennsylvania; Burlington, Camden, Gloucester, and Salem counties in New Jersey; and Newcastle County in Delaware. A population of nearly 2,000,000 is embraced within these limits. The location and general relations of the district are shown in fig. 1, on the next page. In this paper will be discussed the topography, rainfall, run-off, and stream discharges of the chief hydrographic basins, the geology and water-bearing horizons, and the water power and water supply in relation to its present and future utilization.
