Nice antique partners table desk: column legs 2 drawer

This antique partners desk was purchased in a Washington DC antique store about ten years ago.  It is unmarked (except for the numbers shown on the bottom), and features four nice Greek revival styled legs of architecturally correct columns.  One leg unscrews for fitting the large desk into a doorway, etc.   The desk features two very large drawers, one on each side that are shallow, but extend the entire half of the table/desk.      

The desk is 3 feet wide by 5 feet long by 30 inches tall.  The drawers are  each 2 feet wide by 28 inches long.  The table legs each have a small caster on the bottom made of medal that are likely not original, but are concealed under the round base.  The dark finish is in ok shape, but the table top has several dings and small round divits from use It shows its age, but aesthetically is quite nice...we used it as a dining room table in fact.  Each leg has some dings, too, from chairs pulled under the desk, I believe.

I'm not certain of the age, but my guess would be the 1870s or 1880s, but perhaps much earlier.  (Advise welcome!)

Desk is located in Charles Village neighborhood of Baltimore, Maryland.  Local pick up only.