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Structural geology-Continued. Page

• Marathon Basin-Continued. 130
  • Southeastern part of Marathon Basin
    • General features 130
    • Hells Half Acre fault 130
    • Structural features south of Hells Half Acre fault 130
  • General structural problems in the Marathon Basin 131
    • Theoretical problems of the overthrust faults 131
    • Theoretical problems of the steep thrust faults 132
    • Theoretical problems of the tear faults 132
    • Theoretical problems of the folds 132
  • Age of the deformation 134
  • Regional relations of the structural features at Marathon 136
• Structural features of the Glass Mountains 138
• Post-Cretaceous structural features 138
  • Eastern margin of the Marathon dome 138
  • Western margin of the Marathon dome 138
  • Age of the Marathon dome 139
  • Regional relations of the post-Cretaceous structural features 140

Economic geology 141

• Ore deposits 141
• Novaculite 142
• Building stone 142
• Water supply 142
• Oil and gas 142

Index 145

ILLUSTRATIONS

• Page
• PLATE
  • 1. A. View looking southwest from summit of Horse Mountain; B, Housetop Mountain from south 6
  • 2. Correlated stratigraphic sections of pre-Carboniferous rocks of the Marathon Basin 22
  • 3. A, Upper member of Marathon limestone; B, Monument Spring dolomite member of Marathon limestone; C, Woods Hollow shale; D, Upper cherts, limestones, and shales of Fort Pea formation 22
  • 4. A, Vertical layers of Caballos novaculite; B, Basal conglomerate of Maravillas chert at Rock House Gap; C, Maravillas chert at Rock House Gap; D, Detail of lower novaculite member of Caballos novaculite 22
  • 5. A, Gap on novaculite ridge south of old Fort Pea Colorada; B, Maravillas chert northeast of gap shown in A; C, Novaculite ridge southeast of Hackberry Tank; D, View southwest from Hackberry Tank; E, Axial anticlinal valley in Woods Hollow shale at southeast end of Simpson Springs Mountain 22
  • 6. A, East Bourland Mountain from southeast, from northeast end of Simpson Springs Mountain; B, East Bourland Mountain from northeast; C, West Bourland Mountain, looking northeast 22
  • 7. A, B, Novaculite ridges in Lightning Hills; C, Folding in novaculite on east side of Maravillas Creek at Maravillas Gap 22
  • 8. Correlated stratigraphic sections of Pennsylvanian rocks of the Marathon Basin 54
  • 9. A, Massive sandstone of upper part of Tesnus formation; B, Sandstones and shales of lower part of Haymond formation; C, D, Shales and sandy shales of upper part of Haymond formation 62
  • 10. Geologic map of boulder beds of Haymond formation in eastern part of Marathon uplift 62
  • 11. A, Block of novaculite in boulder-bed member of Haymond formation; B, Waterworn cobbles of Dimple and Gaptank limestones in first conglomerate member of Gaptank formation; C, Exposures of boulder-bed member; D, Rounded boulder of brecciated chert from Caballos formation in boulder-bed member; E,Boulder of novaculite in boulder-bed member; F, Boulder of Pennsylvanian limestone 62
  • 12. Correlated stratigraphic sections of Comanche series on the east and west sides of the Marathon Basin 110
  • 13. A, Black Peak in the Del Norte Mountains, from the northeast; B, Del Norte Gap from summit of Del Norte Mountains to the north; C, Black Peak from the south; D, North end of Housetop Mountain 110
  • 14. A, Limestones of Glen Rose formation intruded by igneous rock; B, Limestones of Glen Rose formation of the Maravillas scarp, dipping south off Marathon uplift 110
  • 15. Structural map of Marathon region 118
  • 16. Map and structure sections of Dugout Creek area In pocket
  • 17. Aerial photograph of northeastern part of Dagger Flat anticlinorium 118
  • 18. Aerial photograph of area of Carboniferous rocks south of Haymond station 118
  • 19. Block diagrams showing folded overthrusts of Dagger Flat anticlinorium 126
  • 20. Hypothetical block diagrams showing progressive development of structural features in Marathon region 126
  • 21. Structure sections of Monument Spring and Marathon quadrangles In pocket
  • 22. Map of trans-Pecos Texas showing principal structural features 134