HEIGHT = 5 3/4 inches
WIDTH = 7 inches
VALUE = $300 - $400

Marking on Frontside:
(Engraved on a Rock)
MT VERNON
30
MILES
See View "M"

Marking on Backside:
B&H

Note 1:
The intent of this scene might have been "Washington traveling home and passes a rock engraved with "Mt Vernon 30 miles".

Note 2:
This has the shape of a bookend, but the 2 bumpers on the backside prove it's a doorstop.