. Report of the geological exploration of the fortieth parallel . ancient neijrhboring-rocks are the Uinta quartzites, has retained its natural level, while the Pinonanticlinal has been lifted from a great depth, exposing the lower the east-and-west break described, another powerfid fissure passesin a meridional direction alon- the eastern base of the ranofe. From out ofboth these cracks an enormous trachytic flood has been ejected, surroundingand burying the edges and ends of the uplifted Pinon strata. In DixiePass the sharply eroded edges of the Palaeozoic strata plunge sudden
. Report of the geological exploration of the fortieth parallel . ancient neijrhboring-rocks are the Uinta quartzites, has retained its natural level, while the Pinonanticlinal has been lifted from a great depth, exposing the lower the east-and-west break described, another powerfid fissure passesin a meridional direction alon- the eastern base of the ranofe. From out ofboth these cracks an enormous trachytic flood has been ejected, surroundingand burying the edges and ends of the uplifted Pinon strata. In DixiePass the sharply eroded edges of the Palaeozoic strata plunge suddenlydown beneath a series of rolling trachytic hills, which sweep aroundsouthward, coming in contact successively with the Devonian and the Silu-rian of the western half of the Pinon anticlinal, then with the Cambriannucleus of the fold, and afterward to the south bounding the Silurianand Devonian of the easterly dipping member of the group. There is no-where a more interesting instance of the direct and obvious connection of TJ S Gecl IxdI PLATE XIX. TKAOUvrES. 597 volcanic eruption with mountain dislocation. The trachytes thus exposedextend about twelve miles north-and-south and four to six miles east-and-west, the surface being high, rolling ridges and spurs, those bordering onDixie Valley forming a chain of characteristic dome shapes. Along theiieastern margin for a considerable distance these trachytes overlie the up-turned calcareous shales of the Green River Eocene, and to the south arethemselves oveilaid by a subsequent flood of rhyolite and the horizontalPliocenes of Huntington Valley. The higher spurs and domes all show arounded form and an absence of aiay conspicuous bedding. The general char-acter of the predominating eruption was that of broad, massive accumula-tions, and even the most isolated and conoidal of the trachyte domes showno evidence of the structure of a true volcano. The main material, and thatof all the later eruption, is of biownish and red
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