ZhangShu states, Earth is the mother of Qi. Qi is the mother of water. Where there is Qi there is water. Therefore Earth has 5 elements, called 5 elements Earth or WuTu.
Qing Nan Jing states, heaven depends on form, earth depends on Qi. Heaven Qi has images, Earth Qi has form. The classics also stipulate, HETU which is the principle and LOSHU the application conforming the 8 Gua. 4 cardinals and 4 ordinals.
The cardinals of ZHEN (wood), DUI (metal), LI (fire) and KAN (water) is HETU, principle governing the 4 elemental frames. Matching mountain with water according to these frames form the tenets of Fengshui application – XIAO SHA NA SHUI, blocking and bringing in water. Based on these principles come the followings: -
Kun Ren Yi also referred to its double mountain of Shen Zi and Chen. Wen Qu is water element, thus referring to water frame structure of the 4 major water gates, with birth at Kun Shen, prosperous at Ren Zi and Grave at Yi Chen.
Gen Bing Xin also referred to its double mountain of Yin Wu and Xu. Lian Zheng is fire element, thus referring to fire frame structure of the 4 major water gates, with birth at Gen Yin, prosperous at Bing Wu and Grave at Xin Xu.
Xun Geng Gui also referred to its double mountain of Si You and Chou. Wu Qu is metal element, thus referring to metal frame structure of the 4 major water mouths, with birth at Xun Si, prosperous at Geng You and Grave at Gui Chou.
Qian Jia Ding also referred to its double mountain of Hai, Mao and Wei. Tan Lang is wood element, thus referring to wood frame structure of the 4 major water mouth, with birth at Qian Hai, prosperous at Jia Mao and Grave at Ding Wei.
These verses established the matching water to mountain, in the establishment of the sitting of the XUE. Notice that there is no mention of the Earth frame. Earth being at the center has no direction. When there is Qi there is water, implied that Earth follows the son, which is water. Earth frame takes the water frame.
In ZhangShu, it is noted that Heavenly QI, being external cannot be established. Therefore the QI in every stems cannot be established. Earth QI, being internal established as seasonal nodes can be established.
These speaks of changes in the beginning, where the 8 Heavenly QI from stems matching 12 Earthly QI from the branches, matching with the 4 ordinals GUA make up the 24 subsectors of the 8 trigram of a Later Heaven arrangement for application.