Note 137 — {251} LETTER XXI

Mammoth Cave, about ninety-five miles south-west of Louisville, was accidentally discovered by a hunter in 1809. At the present time two hundred and twenty-three of its avenues have been explored, making a total length of one hundred and fifty miles. During the War of 1812-15, salt was manufactured from the nitrous earth in its caverns, and transported across the mountains to Philadelphia and Baltimore. The close of the war rendering this industry unprofitable, the cave has since been used only for exhibition.—Ed.