XXVlii GEOLOGY OF THE HIGH PLATEAUS. 



CHAPTEE V. 



Page. 

 Speculations concerning the causes of volcanic action 113 



The probable locus of volcanic activity. — Volcanism inconsistent with the notion of an all -liquid 

 interior. — Localization of (he phenomena. — Independence of vents. — Comparison of lavas with 

 metamorphic rocks. — Synthetic character of basalt. — Dynamical causes of eruptions. — Local 

 increments of subterranean temperature. — Mechanics of eruption. — Application of hydrostatic 

 principles. — Explanation of the sequence of eruptions. — A compound function of tempera- 

 ture, density, and fusibility.' — Discussion of the hypothesis. — Exceptions and anomalies. — The 

 ultimate cause unknown. 113-142. 



CHAPTEE VI. 



Sedimentary formations of the District of the High Plateaus 143 



The Paleozoic. — The Shiuarump or Lower Trias. — The Vermilion Cliffs or Upper Trias. — The Ju- 

 rassic. — The Cretaceous. — The Eocene. 143-159. 



CHAPTER VII. 



The Wasatch Plateau 160 



Its structure. — Strata composing its mass. — The great monoclinal. — Gunnison Valley. — Salina 

 Cation. — The Jurassic Wedge. — San Pete Plateau.— Sedimentary beds of the Wasatch Mono- 

 cline. — Bitter Creek, Lower and Upper Green River beds. 160-168. 



CHAPTEE VIII. 

 The Tushar 169 



Sevier Valley from Gunnison southward. — General structure of the northern part of the range. — 

 Its intermediate character between the basiu and plateau types. — Rugged character of the 

 northern portion. — Bullion Canon. — Ehyolitic eruptions. — Southern portion of the Tushar. — 

 The great conglomerates. — History of the range. — Alternations of volcanic activity and re- 

 pose. — The Tushar fault. — Succession of eruptions. 169-187. 



CHAPTEE IX. 



The Markagunt Plateau 188 



General description. — Dog Valley and its eruptive masses. — Bear Valley. — Little Creek Peak. — 

 Tufas and conglomerates. — General surface of the Markagunt. — Succession of eruptions. — 

 Basalt fields. — Panquiteh Lake and recent basaltic outpours. — Sedimentary formations. — Out- 

 look from the southern verge of the plateau. lSti-210. 



CHAPTER X. 



Sevier Valley and its alluvial conglomerates 211 



Upper Sevier or Panquiteh Valley. — Panquiteh Canon. — Circle Valley. — Origin of Circle Val- 

 ley. — Modes of accumulation of conglomerates. — Alluvial cones. — Identity of origin of the old 

 conglomerates and the alluvia now accumulating in the valleys. 211-224. 



