How the laccolites are distributed within these limits is more readily comprehended by the aid of a diagram. In Figure 50 the triangles mark the horizons of determined laccolites, and the crosses the horizons which the invisible laccolites cannot exceed. For example, the base of the Scrope laccolite is visible and is seen to lie on the Tununk shale 400 feet above the Henry’s Fork conglomerate; to represent it a triangle is placed at about the middle of the space representing the Tununk shale, and in the column devoted to the Ellen cluster. The upper surface of the Geikie laccolite is visible and upon it rest, first a few feet of Flaming Gorge shale, and then the Henry’s Fork conglomerate; to represent it a triangle is placed near the top of the Flaming Gorge space. The crown of the Pulpit arch has been so far eroded that half of the Vermilion Cliff sandstone is shown in section, but no laccolite is revealed. It is evident that the Pulpit laccolite is lower than the middle of that sandstone; and to represent it a cross is placed below the middle of the Vermilion Cliff space and in the column devoted to the Hillers cluster. [Illustration: FIG. 50.—Diagram of the Vertical Distribution of the Laccolites of the Henry Mountains. ] The first feature which this graphic assemblage yields to the eye is that there are at least two zones of laccolites. The upper ranges from the lower part of the Blue Gate Group, through the Tununk and Henry’s Fork, to the upper part of the Flaming Gorge Group. The lower has not yet been fully developed by erosion, but its proximity is indicated. The Hillers laccolite is uncovered at top, and the dikes of the Ellsworth, the Greater Holmes, and the Crescent have been reached. All of the invisible laccolites indicated in the Vermilion Cliff and Shinarump spaces must be referred to this zone; and there is reason to suspect that all but one of the invisible laccolites whose indication falls in the Tununk and Flaming Gorge spaces belong also to the lower zone. However this may be, it is not probable that the determination of the depths of the invisible laccolites would vitiate the conclusion that there is an upper zone of laccolitic frequency which is separated from a lower zone by an interspace of laccolitic infrequency. Another feature illustrated by the diagram is that all the determined laccolites are inclosed by soft beds. They have been intruded into the shales, but not the sandstones. They cluster about the Henry’s Fork conglomerate, but none of them divide it. This selection of matrix is confined however to the laccolites and is not exercised by sheets and dikes. Trachyte sheets were seen within the Henry’s Fork, the Gray Cliff, the Vermilion Cliff, and the Aubrey sandstones.