Huge and massively heavy ironstone china platter or tray, antique English ironstone in the Tea Leaf pattern. The marking is Mellor, Taylor and Company - Warranted Stone China.
This measures 18" x 14 1/4" over the rim, and 13 1/2" x 9 3/4" over the well. There's a good sized chip to the underside of the rim, but no cracks or structural damage.