The Newcastle and Frenchtown Railroad, in New Castle County, Delaware, was
partially built with stone ties.  The change from stone ties to wood ties
occurred during the construction of the railroad, so that one end has stone
ties and the other end has wood ties.
 
For additional information, you can contact the Delaware State Historic
Preservation Office, P. O. Box 1401, Dover, DE, 19903 (they don't have e-
mail) f or a copy of the National Register nomination.  Scharf's History of
Delaware (1888) has an excellent discussion of the change in technology.  It
has been reprinted, so you should be able to get it through interlibrary
loan.  There has also been an article on the railroad in DELAWARE HISTORY.  I
don't have the reference, but it should be in the NR nomination, or you can
call the Delaware Historical Society in Wilmington, DE.