The caves were mined for salt-peter back in the Civil War. Salt-peter is potassium nitrate formed by the bat guano that accumulated in the cave over hundreds of years. The Salt-peter was then converted into gunpowder. You have to mine out the salt-peter, mix it with water and ashe in these big bowls and allow the water to evaporate away leaving crystal gunk that needs to scraped off and sent to be made into gunpowder. This trip confirmed the fact that everything was impossible back in the old days!