The erosion of the mountains has given the utmost variety of exposure to the laccolites. In one place are seen only arching strata; in another, arching strata crossed by a few dikes; in another, arching strata filled with a network of dikes and sheets. Elsewhere a portion of the laccolite itself is bared, or one side is removed so as to exhibit a natural section. Here the sedimentary cover has all been removed, and the laccolite stands free, with its original form; there the hard trachyte itself has been attacked by the elements and its form is changed. Somewhere, perhaps, the laccolite has been destroyed and only a dike remains to mark the fissure through which it was injected. CHAPTER III. DETAILED DESCRIPTION OF THE MOUNTAINS. MOUNT ELLSWORTH. It has already been stated that the strata about the bases of the Henry Mountains are nearly level; but the country which is built of them is far from level. The arrangement of the drainage lines has caused the degradation of some parts to greatly exceed that of others, so that while the district at the south, which borders the Colorado River, is paved with the red sandstones of the Jura-Trias series, the adjacent region at the north still carries the yellow sandstones and blue shales of the Cretaceous series. All about Mount Ellsworth are the upper strata of the Jura-Trias. The lower beds of the same series rise upon its flanks and arch over its summit.