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…inward crackings, as it were, of burning and blazing fires, and sounds of waters; as in the Phlegraean Hills, which surround the Vulcanian Plains, commonly called Sulpharata (or Land of Sulphur) is to be seen and heard. Also the Sybell’s Den at Cuma, not far distant; and most mighty horrid Gapings and Recesse, impenetrable, and not to be entred, for their …
https://www.wichita.edu/academics/fairmount_las/geology/wparcell/Kircher/volcanoes/chapter3.php