Not one above another, but one beside another, as the frankincense put upon each, Leviticus 24:7, shows. The pure table was so called because it was covered with pure gold, Exodus 25:24, and because it was always to be kept very pure and clean by the care of the priests.
Related Commentaries of Leviticus 24:6
Leviticus 24:6
6 And thou shalt set them in two rows, six on a row, upon the pure table before the LORD.