. Annual Reports of the Department of the Interior for the Fiscal Year Ended June 30, 1900--Twenty-First Annual Report of the United States Geological Society. p. 821. ^Haydens Report, 1875, U. S. Geol. and Geog. Surv. Col. and adjacent Terr., p. 272, PI. XLVI, fig. 2. REVIEW OF PUBLISHED THEORIES. 285 of ab-sorption of the shales, so that at least half of the space throughwhich the trachyte is distributed is occupied >n the crushed andmetaniorphosed fragments of shale. Most observers agree that shalebeds are favorite horizons of intrusion. The intrusions of basalt in Mount Everts, in the Y
. Annual Reports of the Department of the Interior for the Fiscal Year Ended June 30, 1900--Twenty-First Annual Report of the United States Geological Society. p. 821. ^Haydens Report, 1875, U. S. Geol. and Geog. Surv. Col. and adjacent Terr., p. 272, PI. XLVI, fig. 2. REVIEW OF PUBLISHED THEORIES. 285 of ab-sorption of the shales, so that at least half of the space throughwhich the trachyte is distributed is occupied >n the crushed andmetaniorphosed fragments of shale. Most observers agree that shalebeds are favorite horizons of intrusion. The intrusions of basalt in Mount Everts, in the Yellowstone Park,figured by Holmes (tig. H9), show a relation of conduit to intrudedlens or sill, similar on a small scale to that of the subordinate lacco-liths of the Black Hills (compare sections PI. XXI). These basaltmasses are said to be intruded in Cretaceous sandstones, shales, andlignite, the beds dipping 5^ to 13.^ [The intrusions] cross from horizon to horizon, breaking through the beds andpushing them aside, and bending and crushing them in a most remarkable manner.* * * Tlie masses * * * are very irregular in thickness, reaching in places 40. Fie. 99.—Intruded basalts of Mount Everts, Yellowstone Park (Holmes to 50 feet. They lie in rude sheets approximately with the strata, but bearing thestrongest evidence of their intrusive character. The irregular l)ed that outcropsalong the crest of the ridge is in places 40 feet in thickness, but generally falls farshort of Its jjosition in the strata points very clearly to its intrusive does not lie in any one horizon, but breaks across the strata at all angles, crushingthe severed edges back upon themselves. * * * It rests chieHy in a series of coalshales and sandstones. * * * In the heavier masses this l)asalt has a rudelycolumnar structure and weathers down in very small angular blocks. In the thintongues that have been thrust out from the main into the surrounding strata,there is a tendency to f
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