Yeah, the rock codes are the same. It seems absurd to have to load the symbology from another layer. In all the geology software I use you can set up legends to map colours (etc) to specific codes, whether it's rock type, alteration, gold grades, etc etc., and you can apply that legend to any field in a table. So regardless of whether it's "ROCKTYPE" in one table and "LITHO" in another, you can still apply the same legend (provided codes are the same). If this is the best option I guess it'll have to do, but it seems like a major/ludicrous oversight for a mapping software not to be able to generate/store legends in the way I described!