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1906 Practitioner Nov. 623 Baths below 93° F. are, therefore, known as hypo-thermal baths. Baths, with a range of temperature between 93° and 98° F., are sub-thermal, while above 98° they are called thermal.

1922 W. Lindgren in Econ. Geol. XVII. 293 The terminology proposed..would be as follows:..A. Hydrothermal deposits. a. Epithermal. Formed by ascending hot waters near the surface in or near effusive rocks at relatively low temperature and pressure. b. Mesothermal. Formed by ascending hot waters in or near intrusive rocks at intermediate temperature and pressure. c. Hypothermal. Formed by ascending hot water in or near intrusive rocks at high temperature and pressure... The prefix ‘hypo’ has been substituted for ‘kata’ to correspond with Ransome's now generally accepted terms of ‘hypogene waters’, the suggestion implied being that the hypogene waters are principally derived from the region of the hypothermal deposits.

1969 G. M. Bennison & A. E. Wright Geol. Hist. Brit. Isles x. 247 The latter [mineral veins] are of two phases, hypothermal and mesothermal, usually of different and characteristic trend.

1970 C. F. Park & R. A. MacDiarmid Ore Deposits (ed. 2) xii. 294 Many minerals of the igneous metamorphic zone continue without interruption into the hypothermal zone.