Castle Rock.—One of the most interesting works of nature in the state from a geological standpoint is known as "Castle Rock," a natural formation located in Gove county, in the valley of the Hackherry, about 10 miles from its mouth. This castellated mass is composed of a coping of limestone and the shaft of chalk and compact shale. Its unique formation was produced by the shales wearing away, the strongly cemented stone serving as a protection to the upper surface. In this way mountainous appearing masses are frequently produced, especially where various streams cut their way through the hard stone into the softer materials below. Similar formations are met with in Ellis county which show isolated columns which rise from 20 to 73 feet in height.