In the 1860's, this saltpetre mine was worked where vast deposits of bat guano had, by natural decay, become saltpetre, the chief ingredient of gunpowder used in the Civil War. Mixed with small parts of charcoal and sulphur, saltpetre from here powered Confederate cannon and smaller ammunition, and some was shipped east of Mississippi. The bat-inhabited cave, source of the guano, extends about 23 miles, and one room in the great bat den is 585' x 325' with a 45' ceiling. A narrow gauge railway with mule-drawn cars was used in the digging, and the cave had corrals for the mules.