Under rating threshold (hideshow)
The Groups:
1.Life and Death
2.Air
3.Animals
4.Wonders & Construction Items
5.Earth
6.Fire
7.Plants
8.Agriculture
9.Humans
10.Myths
11.Microorganisms
12.Tools and Constructions
13.Transportation
14.Water
Under rating threshold (hideshow)
The game says that limestone+fertilizer=saltpeter but saltpeter is used as fertilizer;it isn't an ingredient in creating saltpeter