Top plate for the square cake stand, Fostoria American pattern glass.
This is crystal clear glass, 10" x 10".
We're not certain if Fostoria ever made these square salvers with metal or silver stands, but we think they probably did at some point... many 20th century glass companies did!
It stands without rocking on it's 'stump', and would make a fine plateau or tray. There's a few tiny fleabite chips to the bottom rim, so we're guessing it's been used as a tray before.