242 GEOLOGY OF THE HIGH PLATEAUS. 



Section V. — Monroe Amphitheater. 



In the middle gorge of the amphitlieater, beginning at 7,750 feet alti- 

 tude and descending to the west. 



Feet, 



1. Granitoid trachyte 110 



2. Augitic andesite, in layers varying miicli in thickness along the exposure. . 200 



3. Hornblendic trachyte, very rough and coarse in texture, probably four or 



five layers 330 



4. Augitic andesite 80 



5. Hornblendic trachyte 40 



6. Hornblendic trachyte . 40 



7. Hornblendic trachyte 70 



8. Conglomerate, with fragments of hornblendic andesite and trachyte and au- 



gitic andesite 55 



9. Hornblendic andesite of unknown thickness in numerous layers, with very 



uneven divisional lines. 



10. Modern alluvial or torrential deposits of unknown thickness. 



11. Tufas, water laid, of unknown thickness. 



12. Hornblendic andesite, possibly forming a part of the same mass as No. 9, 



lying upon the eroded and highly-inclined surface of propylite ; thickness 

 unknown. 



13. Hornblendic propylite, rising in a precipitous wall or barrier far above the 



last-named mass, but also extending beneath it and unquestionably of 

 greater antiquity 775 



Section VI. — Sevier Plateau. 



In a large ravine about 3^ miles south of Marysvale Peak, beginning 

 on the south side of the I'avine and descending westward; altitude, 7,700 feet. 



Feet. 



1. Hyaline trachyte, with a few porphyritic crystals, somewhat resembling a 



liparite, but no free quartz 35 



2. Granitoid trachyte, rather dark gray 22 



3. Granitoid trachyte, dark gray and coarser than preceding 20 



4. Granitoid trachyte 32 



5. Granitoid trachyte 28 



6. Dolerite, with large crystals of plagioclase in -a very fine base 15 



7. Hyaline trachyte, similar to No. 1 25 



8. Hyaline trachyte, bright reddish color 37 



9. Argilloid trachyte, in several layers, varying slightly in character 90 



10. Dolerite in several layers, similar to No. 6, with smaller crystals of plagio- 



clase 75 



11. Argilloid trachyte, in numerous layers' ICO 



12. Tufas of unknown thickness, but a visible exposure of 220 



