A great portion of the soil of western America lies immediately over immense strata of horizontal limestone, in which are numerous fissures. I have often seen the presence of these indicated in Ohio, Kentucky, and Indiana, by hollows in the {256} ground in the form of inverted cones, which are here called sink holes. Some of these fissures have openings to the surface. A stupendous one in Kentucky,[137] known by the name of the great cave, has been explored to the distance of nine miles from its entrance.[138] The nitrate of potash has been found in some of these caves, and the sulphate of magnesia in others. Many of them abound in stalactites of calc sinter; and copious streams of water pass through some of them. One of these in Kentucky turns a subterraneous mill, to which access is obtained by a sink-hole; and a Colonel C---- of Indiana told me that a settler in his neighbourhood, on digging a well, penetrated into a stream of water, and found blind fishes in it.[139] During the last and the present summer, this country has suffered droughts, which the inhabitants consider extraordinary. Between Corydon and the Ohio the water was very muddy. Some people in that part are obliged to carry water from a distance of two miles. It is not uncommon now to see mill streams entirely dried up. I have seen several peach trees, with the fruit nearly ripened, almost dried up by the scorching heat; and, in some instances, the woods assuming the appearance of autumn prematurely, from the same cause. The disadvantage of the want of water will be thought less appalling, when it is recollected that the clearing of the ground has a tendency to increase springs; and when it is considered that {257} the dryness of rivers is not occasioned by the total want of springs, but by the evaporation from the bottoms of water-courses; and farther, that water in most situations may be procured by digging wells. Immediately on the north bank of the Ohio, and about thirty miles below the falls, I crossed an avenue in the woods, 600 or 700 yards wide, which had been devastated by a tornado that had passed from west to east, and in its way cleared the ground almost entirely. The largest trees were either torn up by the roots or broken. In the part that I observed, nothing but underwood and the shattered fragments of trees remained. On making inquiries as to the hurricane, I was informed that it swept over the country to the length of several hundred miles; and that, on the Kentucky side of the river, it totally obstructed a road with timber which has not yet been removed.