wood, as hazel and briars, also with grasses, and an immense variety of deciduous plants.—The name barrens must have arisen from the lands so denominated not producing such a large growth of vegetable matter as the forests, rather than from sterility. They are, in reality, much better pasturages than the woodlands, and, when cultivated, produce the best crops of wheat. I found travelling through the barrens to be somewhat uncomfortable, on account of exposure to the rays of the sun, and the dust of the road, which was continually raised, in a little cloud, by the motion of the horse's feet. This sort of ground is dry, and without the vast quantity of decaying vegetable matters to be seen in the woods, and for these reasons it is probably more conducive to health.
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
