Page:Popular Science Monthly Volume 79.djvu/105

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 showing the method of making the vertical borings, the direction of the first two inclined borings, the positions of the shafts and the extent of explorations. (Adapted from drawings of the Board of Water Supply.)

during an epoch of great continental elevation. The borings in the Highlands have been carried to a depth of 750 feet without reaching the bottom. This is more than twice as great a depth as has been found at any other point either above or below, though even at Pegg's Point and at New York City it is possible that there is a narrower gorge in the middle of the river. The great width and depth of this gorge must have been due to glacial erosion when a stream of ice was forced down from the wide bay that then existed north of the mountains. The syphon tunnel under the Hudson is only one of a number of great syphons and aqueducts that must be constructed between the Catskills and New York City. Owing to the present

 a postglacial entrenchment of Esopus Creek at the Tongore site. The preglacial gorge lies at the north side of the valley buried beneath 250 feet of drift. (Photograph by Board of Water Supply.)