1 The accompanying geological map of Westchester County was prepared by the officers of the United States Geological Survey, at Washington, D. C, from data prepared by Professor Dana, and presents the latest conclusions of that school of geologists who agree with Prof. Dana as to the Lower Silurian age of the Westchester County rocks. The geological portion ol' this cliapter was written at the office of the Geological Survey, at Washington, and eubniitted to Prof. McGee, the chief geologist of the survey, and he has approved it as correct and as full as the present information about the section of country will admit. Prof. McGee says that very little is known of the geological age of Westchester County, and that even that little is not accepted by all geologists. Prof. Newberry, differing with Prof. Dana and the United States Survey, holds that the county belongs to the Laurentian age, while the other side place the county region on the Upper Silurian age. We have given the views of both, and followed with the map. We have used Prof. James D. Dana's account of the limestone beds as the most importiint feature and value which geology points out for the county. Of course we had to abridge as much a.s possible in order to keep within the limits of our work.

'- Prof. I. S. Newberry, in Popular Sci«Ht« Monlhly, for October, 1878.

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Geoloi>ir Map of VV^est Chester Coimty, N.Y.

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