or THE Alleghanies (a spelling now more common than Allegheny), a name formerly used of all the Appalachian Mountains, U.S.A., and now sometimes of all that system lying W. and S. of the Hudson river, being steep and narrow-crested in Pennsylvania (1500-1800 ft.), and in Maryland, Virginia and West Virginia higher (3000 ft.-4473 ft). and with broader crests. Another usage applies to the ridges ("the Alleghany Ridges") parallel to the Blue Ridge; the north-western part of this region is sometimes called the Alleghany Front or the Front of the Alleghany Plateau. The Alleghany Plateau is the north-westernmost division of the Appalachian system; it is an eroded mass of sedimentary rock sloping north-westward to the Prairie and Lake Plains and reaching south-west from the south-western part of New York state through Tennessee and into Alabama.