CHAPTER XI. 

 SEVIEE AND PAUNSAGUNT PLATEAUS. 



General strncture and form of the Sevier Plateau. — Sculpture.— Eavincs. — Superposed features and 

 details. — Northern portion of the plateau. — A gigantic clift".— Monroe Amphitheater. — Lava beds 

 exposed within it. — The Gate of Monroe. — Propylitic masses. — Clastic volcanic beds at the base 

 of the series. — Homblendic andesites. — Intervening period of erosion of the propylites. — Horn- 

 blendic trachytes and augitic andesites. — Argilloid and granitoid trachytes. — General succession 

 of the eruptions. — Comparison with the succession found in the Auvergne. — Eastern side of the 

 Sevier Plateau and Blue Mountain. — Great extent of the emanations from the principal volcanic 

 centers of the northern part of the plateau. — Eroded lava-capped mesas around Salina CaEon. — 

 The Black Cap. — Augitic trachytes. — Lava sheets south of Monroe Amphitheater. — Central vents 

 of the Sevier Plateau. — Volcanic conglomerates. — An ancient cone, burjed in lava and exhumed 

 by erosion. — Conglomerates south of the central vents. — Southern focus of eruptions. — Andesitic 

 conglomerates. — Southern termination of the Sevier Plateau. — General succession of eruptive 

 sheets. — Sections. — East Fork Canon. — Effect of the Sevier fault. — Tufaceons deposits exposed in 

 East Fork Canon. — Their transitional characters. — Their metamorphism and the resemblance of 

 the metamorphs to lava sheets. — Phonolite hill. — Grass Valley, its structure and origin. — Exists 

 ence of an ancient lake in Grass V.alley. — The causes which produced it. — Tufaceons deposits of 

 Mesa Creek. — Their recent formation. — Their transitional characters. — Alluvial cones of Grass 

 Valley. — The Pauusiignnt. — Lower Eocene beds. — Faults. — The southern terraces. — Paria Valley. 

 — A grand erosion. — The scenery of Paria Valley. — Table Cliff and Kaip^rowits Peak. — The Pink 

 Cliffs and architectural forms sculptured from them. — A recent basaltic cone. — Scattered basaltic 

 craters of the southern terraces. 



The Sevike Plateau is next to be described. It is a long and rather 

 nan-ow uphft, having a fault along its western base and inclining to the 

 eastward; at first very gently, then with a stronger slope, which grades 

 rapidly down into Grass Valley. The length of this table is about 70 

 miles, and its width varies from 10 to 20 miles. It is, therefore, long 

 and narrow like the general gronnd-plan of a mountain range. But its 

 structure has very little analogy to ordinary mountain uplifts. It has no 

 sharply upturned strata upon its flanks reclining against a core of meta- 

 morphic rocks — ^no summit ridge marking the axis along which granitoid 

 and schistose rocks have been protruded, nor even the monoclinal ridge 

 which characterizes the Wasatch and Basin Ranges. It is a tabular mass 

 very like the inclined blocks of the Kaibab region to the southward. The 

 inclination is very small, seldom exceeding three or four degrees upon the 



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