This is a great 19th century burr root  table snuff box.  The base has an integral wooden hinged lid, which when opens shows a makers stamp  Geo Sinclair. George Sinclair worked in Edinburgh around 1820-1840.
 Burrs occur on many trees, most commonly at the junction of the trunk with the ground or root. They are caused by a number of small shoots which are unable to break out, and form an interwoven, contorted but unusually stable mass. They can be very ornamental.
It measures approx 10cm l x 9.5cm w at the widest section.