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…the conflicts of air and moisture, in those most dark and deep Regions of the Earth, so remote from all influence of the Sun. Therefore subterraneous fire was necessary in the internal Oeconomy, or constitution of, as it were, the organiz’d parts of the earth, and distribution of Life and heat, as we may so say, to all the exteriour members. Plato…
https://www.wichita.edu/academics/fairmount_las/geology/wparcell/Kircher/volcanoes/chapter1.php