_Laccolites of Other Regions._—In many lands geologists have observed intrusive rocks occurring in great bodies, but I am not aware that such a system as that of the Henry Mountains has ever been described. Doubtless all such bodies are laccolitic, but the combination of conditions which this field presents can rarely be repeated. In the first place the strata which here contain the laccolites lay level. They had suffered no displacement before the epoch of irruption, and they have suffered none since. The laccolitic phenomena stand by themselves, with nothing to mar their symmetry or complicate their study. In the next place the laccolites are here assembled in such number and with such variety of size, form, and horizon that there is little danger of mistaking accidental features for essential. Again, the region having been recently elevated is the scene of rapid degradation. Waterways are deeply corraded, slopes are steep, and escarpments abound. And finally the climate is so arid that vegetation is exceedingly scant. The rocks are for the most part bare and their examination is unobstructed. If the conditions of erosion and climate had been unfavorable in the Henry Mountains, they could not have yielded the key to the laccolitic structure; but the key once found, it is to be anticipated that the structure will be recognized in other laccolites of which the exposures are less perfect. If the strata had experienced anterior displacements so as to be inclined, folded, and faulted, a symmetrical growth of laccolites would have been impossible, and the mountains would not have yielded a knowledge of the type form. But the type form being known, it is to be anticipated that in disturbed regions aberrant forms will be recognized and referred to the type. _Possible Analogues of the Laccolite._—All the arches of the Henry Mountains have been ascribed to laccolites, whether their nuclei were visible or concealed, and the evidence upon which the latter were included appears to admit of no controversy. The question arises whether the great flexures of the Plateau region may not be allied in structure. The volcano having its homologue in the laccolite, may not broad lava fields have their homologues beneath displacements of the Kaibab type? The idea is naturally attractive to one who has made a special study of laccolites, but it is hardly tenable. There are indeed many points of resemblance between such flexures as the Waterpocket, and the uplifts of the Henry Mountains; but the points of contrast are equally conspicuous, and seem to mark a radical difference. There is a certain symmetry of form which is characteristic of the laccolitic arches, but which is rarely seen in the great flexures. And there is a linear element which is characteristic of the latter, but not of the former. The great flexures always have direction or trend, and often exhibit parallelism; the laccolitic arches betray no trend either individually or collectively.