Regency Cylinder roll top desk

I just purchased a cylinder roll top desk which I find quite unique.  They say it was from the Regency period (not even sure if that is a correct classification).  I know it is old because all the drawers are dovetailed, there are roller side doors that are held together with a cloth material, and the top settles onto the desk held in place by dowels.

Can anyone tell from the pictures I have sent in this email what period this piece came from?  Also, it came with a marble top that was cracked in two places.  I am having a new marble piece made exactly to the dimensions and specifications as the original.  Is it a good idea to keep the original marble slab?  Does anyone know what type of wood was used?  It is very heavy. There is also some damage to the front left leg.  I have the trim that fell off, but should I get this professionally restored.  Is it worth the cost to do this?