Petrified Wood

Mix equal parts of gem salt, rock alum, white vinegar, chalk and Peebles' powder. After the mixture becomes quiet, put into it any wood or porous substance, and the latter becomes like stone.

I'm trying to figure out what gem salt and peebles' powder are.

Gem Salt is the old name for colored, highly mineralised,( ususally basalt) rock salt, back before iodized salt was manufactured, and instead, we used sea salt, rock salt, spring salt,....