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Aerial photograph southwest of Blackbird, Delaware, showing the Borthwick area
The Bays And Basins Of Delaware. Overlay map of wells, test holes, and instruments. Explanation, Test hole, Recorder well, Soil pit, Rain gage, Bore hole for pollen study, Numbers indicate well schedules with prefix Gb 45-.; From Rasmussen, W., Geology and Hydrology of the Bays and Basins of Delaware, 1958 , Plate 4B.