LIST OF ILLUSTRATIONS. 



PART I. 



Page. 

 Plate I. Head of Iowa gulch — Iowa amphitheater and Mount Sherman in the background. 

 (Frontispiece.) 

 II. Leadvillc and the Mosquito Range '. 6 



III. SoHtli Park and eastern slopes of Mosquito Range, from Mount Silverheels 28 



IV. Archean phenomena ■;,•> 



Fig. I. Face of cliff, Arkansas amphitheater. 



2. Bowlder, Buckskin amphitheater. 



3. Bowlder, Mosquito gulch. 



V. Red-cast beds (Cambrian). Contorted limestone (Upper Coal Measure) CO 



VI. Blue limestones (specimens showing ribbed structure) C4 



VII. Hornblende-porphyrite sj)ecimens 84 



Fig. 1. From Arkansas dike. 



2. From south wall of Buckskin gulch. 



VIII. Nevadite from Chalk Mountain 86 



Fig. 1. Micro-section of White Porphyry. 



2. Micro-section of Nevadite. 



3. Specimen of Nevadite. 



IX. Mount Lincoln Massive from Mount Silverheels 94 



X. Mosquito Range and Blue River Valley, looking north from Mount Lincoln 98 



XI. Summit of Mount Lincoln and north wall of Cameron amphitheater (upper end).. 112 

 XII. North wall of Cameron amphitheater (lower end) 114 



XIII. South side of Buckskin gulch 128 



XIV. Cliffs on north side of Mosqnito gulch (showing fault and intrusive masses of por- 



phyry) 132 



XV. Sacramento arch (looking across Big S.acramento gulch from Pennsylvania Hill) . 148 



XVI. North side of Horseshoe gulch (showing White Ridge aud laccolite) 154 



XYII. Head of Four-Mile Creek (showing the "Horseshoe") 158 



XVIII. Sheep Mountain fold and London fault (south side of Horseshoe gulch) 164 



XIX. Rhyolite and porphyry, Chalk Mountain 196 



Fig. 1. Plan of eastern edge of mountain, showing quartzite and porphyry 

 dike inclosed in rhyolite. 



2. North side of railroad cut, at south end of Chalk Mountain, showing 



porphyry cutting through sandstone. 



3. South side of same cut. 



XX. Micro-sections of porphyrite. Appendix A 336 



Fig. 1. Biotite-porphyrito (Type VI) from North Moscfliito amphitheater. 



2. Hornblende-porphyrite (Type VII). 



3. Hornblende-porphyrite (Type V) from Buckskin gulch, showing large 



hornblende. 



4. Hornblende-porphyrite (Tyjje V) showing small needles of hornblende. 



XXV 



