The eight main hot-spring areas of eastern Taiwan, distributed in a belt 185 mi (300 km) long and 25 mi (40 km) wide, can be classified, according to their geologic and chemical characteristics, into three groups: (1) the Eocene slate, phyllite, and quartzite group, (2) the Miocene sedimentary rocks of the Coastal Range group, and (3) the Miocene argillite, slate, and phyllite group. Most of the springs belong to (3).

The laboratory analyses of the hot water and rock samples from the eight springs, performed for this paper, accompanied by earlier chemistry and temperature reports on water from these springs, reveal that little deviations in their characteristics exist for each spring, although the water temperatures have fluctuated.

The SiO₂ concentration geothermometer of the mixing model (Fournier and Truesdell in 1977) and a modified mixing model, accomplished for this paper, are presumably the best available to estimate the geothermal reservoir temperature. Their application, however, cannot be valid in the greenschist region. This fact should not deteriorate the accentuated exploration of the geothermal energy in eastern Taiwan. Meanwhile, the establishment of an alternative geothermometer for the greenschist region is desired.

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