Geological Survey Bulletin 1265 Ancient Lavas in Shenandoah National Park Near Luray, Virginia

Cover

Abstract

Introduction

General geology
   Structural setting
   Rocks underlying the Catoctin Formation
   Rocks overlying the Catoctin Formation
   General character of the Catoctin Formation

Catoctin Formation
   Structure
   Sedimentary members
   Volcanic flows
   Primary features
      Columnar jointing
      Low-dipping primary joints
      Amygdules
      Sedimentary dikes
      Flow breccias
   Petrography and mineralogy of the flows
   Dikes of greenstone
   Purple volcanic slate
   Original nature of the Catoctin lavas

Conclusions

References cited

PLATE

1. Geologic map and sections of the Blue Ridge near Luray, Va

FIGURE

1. View of the Blue Ridge from the west

2. Generalized geologic map of the Catoctin Mountain-Blue Ridge anticlinorium in Virginia

3. Index map of the area described in this report

4. Diagrammatic stratigraphic section showing relations between the Catoctin Formation and the granitic basement rocks

5. View of Franklin Cliffs from Big Meadows Campground

6. Photograph of upper falls in Whiteoak Canyon

7. Photograph of schistose greenstone along the Appalachian Trail

8. Geologic sections of the lower three flows in the Catoctin Formation

9. Photographs of columnar jointing in greenstone

10. Photograph and photomicrograph of amygdules in greenstone

11—15. Photographs of:

11. Sandstone dikes in greenstone

12. Sawed slab of amygdaloid breccia

13. Mud-lump breccia

14. Sawed slab of porphyritic greenstone

15. Greenstone dikes in basement rocks

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UNITED STATES
DEPARTMENT OF THE INTERIOR
STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY
WILLIAM T. PECORA, Director

Library of Congress catalog-card No. GS 68—304

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