One area can be divided into several sections, matching to those of country rocks, by pH or Eh of groundwater.
The author introduced three examples, the above was true.
1) The Yumoto valley in Ikaho spa, Gumma Pref. is clearly divided into two by the reduction rate of pH at cooling and the value of Eh of thermal waters.
2) The Hebino river basin in Gumma Pref. is divided into five pH sections. And the Quaternary lacustrine deposits area is distinguished from the area of base rocks, consisting of green tuffs and andesites of Miocene period, by low values of pH and high values of Eh of groundwaters.
3) The Atsumi hot springs district, Yamagata Pref. is divided into four, i. e., northeastern mountains, northwestern mountains, alluvial plain and southern mountains, all which are related to the country rocks respectively, by the values of Eh of groundwaters.
In conclusion, the author proposes the significance of Eh measurement of groundwater.