This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Earth Branches gathers the four of the twelve Earthly Branches whose own fixed agent is Earth: Chou the Ox, Chen the Dragon, Wei the Goat and Xu the Dog, one at the close of each season.
All four share a structural role the other eight branches do not: each is a storehouse branch, holding three hidden stems (canggan) rather than the one or two a cardinal or growth branch carries, and each serves as the vault of a different trine. Chou, governing late winter and the hour before dawn, banks Ji as its principal qi alongside Gui and Xin and so becomes the vault of the Metal trine; Chen, closing spring, banks Wu alongside Yi and Gui and becomes the vault of the Water trine; Wei, closing summer, banks Ji alongside Ding and Yi and becomes the vault of the Wood trine; Xu, closing autumn, banks Wu alongside Xin and Ding and becomes the vault of the Fire trine. Between them the four Earth branches sit at the hinge of every season, cold and damp in Chou, fertile in Chen, warm and dry in Wei, warm and closing in Xu, and each is read in the Four Pillars as a reservoir that can lock its stored agent away or release it, depending on what the rest of a chart calls for.
No animal is attached to any of the twelve branches in the earliest layer of the tradition. The oracle-bone inscriptions use the branches purely to count the days of a sixty-day cycle, combined with the ten Heavenly Stems; the animal each branch now carries, Ox, Dragon, Goat and Dog among them, was attached later, to the branch rather than derived from it.