"Nearly all the leading mines on the Comstock are down to where the rock is exceedingly hot ... As the Savage [mining] Company has started up machinery capable of sinking to the depth of 4,000 feet, it will presently be in danger of dropping into the great central fires of the earth."
The Big Bonanza: An Authentic Account of the Discovery, History, and Working of the World-Renowned Comstock Lode of Nevada - Dan de Quille

P. 386


Another reason I love this author. He's serious, too! Oh, the eighteenth century...