Antique Ladies Secretary Writing Desk

(NOTE: the attached photo is not the best. The desk is placed in front of another antique wood piece so it can be deceiving. If necessary I could retake pics. thanks)
I want to sell this piece, but I am uncertain of its period, age, etc. hence, value.
Antique mahogany??? ladies' slant drop front desk/secretary. I am unsure of the wood because I do not want to ruin the piece in any way. The interior would lead me to believe it is a fancier walnut or mahogany.
Shaped front legs.
Pigeonholes & one small drawer (missing knob) inside for filing.
It appears there was a backsplash and sides attached at one point. There remains just the side of the backsplash atop the desk (see pic).
One hand dovetailed long drawer (under slant front) with brass handles.
Slant front has brass key hole and opens with brass adjustable chain at each side.
Measures appx. 30" wide (widest part of slant front) x 29" deep opened front/13" deep unopened front x 48" high. 
Age Unknown. I've been researching almost everywhere I can think of...I can't find anything parallel to this desk. What sets this apart from what I am finding is the brass finishes (including the chains.)
Though some of the wood scrolling is off, this piece is in very good condition. she's sturdy and solid, but elegant.
It is in nice condition but needs a little cleaning up. I am unwilling to alter the finish in any way so as not to diminish value.