In researching possible new modules for my subway layout, I've learned that before the Dual Contracts of 1917, the BRT had constructed a 4th Avenue subway shortly after the first IRT line opened. The station mosaics and construction details were similar in style to the Beaux-Arts designs of the 1904 IRT lines. A few of the stations still have round columns like the IRT.
Unfortunately, in the 1970's, the 4th Avenue stations received a makeover that buried the original details under large modern tiles. Bits of the original details peek out from underneath, but not enough to form a basis for modeling.
Does anyone know of a book that might show the original station details of the 4th Avenue stations?
