The breadth of the county varies from twenty-five to eight and one-half miles. Throughout its entire extent along the Hudson the Westchester shore rises abruptly from the river edge to elevations seldom less than one hundred feet. Nowhere, however, does the Westchester bank ascend precipitously in the manner, or even at all resembling the manner, of the Palisade formation on the western shore. The acclivity is often quite sharp, but everywhere admits of gradual approach, for both pedestrians and carriages, to the high ridges. Thus the whole western border of the county both affords a splendid view of the entrancing panorama of the Hudson, and is perfectly accessible from the railroad, which runs along t he bank of the river. Moreover, beyond the ridges in the interior the land lias a uniform and gentle descent into lovely valleys, which permit convenient and rapid travel from all directions. These physical conditions render the western section of the county one of the most inviting and favored localities in the world for costly residences and grand estates; and from the earliest period of European settlement of this portion of America, the Hudson shore of Westchester County has been a chosen abode for families of wealth and distinction. But every other part of the county -- at least every part conveniently reached from the railroads -- is also highly esteemed for select residence purposes; and, indeed, Westchester County throughout its extent is peculiarly a residential county. Spuyten Duyvil Creek and the Harlem River, which separate Manhattan Island from the mainland and form a portion of the southern boundary of the old County of Westchester, are in reality only an arm of the sea: and though to the superficial observer they may appear to constitute one of the mouths of the Hudson, they have no such function, and, indeed, receive none of its flow.