Geology of the Elkton area Virginia GEOLOGICAL SURVEY PROFESSIONAL PAPER 230 Geology of the Elkton area Virginia By PHILIP B. KING GEOLOGICAL SURVEY PROFESSIONAL PAPER 230 A detailed report on an area containing interesting problems of stratigraphy', structure, geomorphology, and economic geology UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1950 UNITED STATES DEPARTMENT OF THE INTERIOR Oscar L. Chapman, Secretary GEOLOGICAL SURVEY W. E. Wrather, Director For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. - Price $1.75 (paper cover) CONTENTS Page Page Abstract-- _ ________________________________________ 1 Stratigraphy—Continued Introduction. ______________________________________ 1 Cambrian system—Continued Previous work. _ ____________________________________ 2 Elbrook dolomite.________-_____._--_-__-__. 32 Present work. ______________________________________ 3 Name._ _____________-_-_-____---_____- 32 Acknowledgments. _________________________________ 3 Outcrop.____-___-------_--___----.-___ 32 Geography.. _ ______________________________________ 4 Character, _____________________________ 32 Stratigraphy _______________________________________ 6 Age_.____-_..-__-_---_--___------_-_._ 32 Pre-Cambrian rocks__ . __________________________ 7 Residuum of Elbrook dolomite ___________ 33 Injection complex. __________________________ 8 Stratigraphic relations-__________________ 33 Name. _ ----_-______----________-_-_-__ 8 Conococheague limestone.___________________ 33 Outcrop. ______________________________ 8 Name __-__________-_--______---------_ 33 Character and origin. _ __________________ 8 Outcrop.-___-_-_-_------__-_---------- 33 Jointing and weathering. _ _______________ 9 Character_ _.-_____.-_________--__---_ 33 Greenstone intrusives in injection complex. 9 Age._-____-______-------__-__--------- 34 Occurrence of blue quartz in rocks of injec­ Residuum of Conococheague limestone-___ 34 tion complex. ________________________ 9 Stratigraphic relations.__________________ 34 Swift Run formation ________________________ 9 Ordovician system._____________________________ 35 Name_ _ _----______---_--_________-____ 9 Beekmaiytown dolomite (including Chepultepec Outcrop _-__---__-__-__--____-___-___-_ ia limestone) _______________________________ 35 General features, _______________________ 10 Name _________________________________ 35 Local features. _________________________ 10 Outcrop-______________________________ 35 Stratigraphic relations- _ _________________ 11 Character___ _ __________________________ 35 Regional relations __ __________________ 11 Fossils.—_ — -__ __--------------------_ 36 Catoctin greenstone- ________________________ 12 Weathering features of Beekmantown Name _________________________________ 12 dolomite. __.-_-_____-___-_____--___-_ 36 Outcrop- -____________________________'_ 12 Stratigraphic relations__________-_-_--___ 37 Character____ _ _________________________ 12 Limestones of Middle Ordovician age_-_---_-_- 37 Thickness and stratigraphic relations- _____ 13 Outcrop.________________.____----_--__ 37 Regional relations of unconformity above Classification. __ ________________________ 37 Catoctin greenstone- __________________ 13 Character_________________________ 38 Age____- ------______-________.________ 14 Stratigraphic relations.__________________ 38 Cambrian system- _ _____________________________ 14 Martinsburg shale__________________________ 38 Chilhowee group_ ___________________________ 14 Silurian system.._______________________________ 39 Name. ________________________________ 14 Sandstones of Silurian age.__________________ 39 Description by Rogers___ _ _-_-____-_--___ 15 Triassic (?) system______________-_______-_______ 39 Subdivisions. __________________________ 15 Intrusive igneous rocks________-___--_----_-_ 39 Loudoun formation. ___-_____-___-_-____ 16 Tectonics.____________--_______-_-_-_-__----_--____ 39 Weverton formation. _____ ____.-__--___-_ 17 Structural features of pre-Cambrian age__._-___.__ 39 Harpers formation. ... __________________ 19 Relations of pre-Cambrian rocks to Chilhowee Antietam quartzite __ _ _ _________--.___- 20 group._ _________________________________ 39 Broader relations of Chilhowee group_-___- 23 Interpretation of structural features of pre- Tomstown dolomite.. _ ______________________ 24 Cambrian age_ _______-_-___-.____-____--- 41 Name _-_-___-______--_-____-__________ 24 Structural features of late Paleozoic (Appalachian) Outcrop __-_-___-____-_-_________-___-_ 24 age________________.____-__-_-_-_----_-.__- 41 General features. _______________________ 25 General character.-_____________________ 41 Age.--_ ----_-----__-__--__-_-__---__-_ 25 Discussion of illustrations._______________ 42 Tomstown dolomite in outcrop. __^_______ 25 Description of larger structural features _______ 42 Subsurface Tomstown dolomite.. _________ 26 Shenandoah Salient-____________________ 42 Basal beds of Tomstown dolomite__----__- 28 Area north of Shenandoah Salient-________ 43 Residuum of Tomstown dolomite ____--__. 28 Area west of Shenandoah Salient-________ 43 Stratigraphic relations- __________________ 30 Elkton Embayment_-._________---____-. 44 Waynesboro formation ______________________ 30 Hanse Mountain area.__________-__-_--_ 44 Name. ________________________________ 30 Area northwest of Hanse Mountain area_ 45 Outcrop. ______________________________ 30 Interpretation of larger structural features. _ _ _ _ 45 Character _ _ _______________________ _ _ 30 Restoration of structure above and below 31 surface-_____________________________ 45 Residuum of Waynesboro formation. 31 Interpretation of Stanley fault__________ 47 Stratigraphic relations- ____________ 32 Problem of "Blue Ridge overthrust" ______ 47 m IV CONTENTS Page Page Tectonics—Continued Economic geology—________________________________ 63 Structural features of late Paleozoic—Continued Iron and manganese________________-_----___-_ 63 Special structural features___________________ 50 General character of deposits_______________ 63 Slaty cleavage________________________ 50 Summary of production_________________ 63 Jointing and veining____________________ 51 Reserves__ _ ________________----___--_ 64 Rock flowage and disharmonic folding. _ _ _ _ 51 Occurrence__ _________________________ 64 Gravity data________________-____________-_ 52 Character_ _______________-------_-___ 65 Cenozoic deposits and land forms.____________________ 52 Origin. ________________________________ 65 Upland areas___________________________________ 53 Mines.____________________________________ 66 Possible high-level peneplains ________________ 53 Stanley mine.______________-_-_---___._ 66 Character_ _ __________________________ 53 Honey Run mine_____________--_---____ 67 Age_ _ _________________________________ 54 Ingham mine_________________________ 67 Possible intermediate peneplain.______________ 54 Little ore bank_________________________ 68 Operations of Shenandoah Iron Works___ 68 Valley floor.___________________________________ 54 Smith bank____-_-___-_____________ 69 Residuum. _ _ _____________________________ 54 Boyer mine.___________-___---_---_____ 70 Character. ____________________________ 54 Kimball bank_____________________-_-__ 70 Thickness____ _ _________________________ 54 Baker bank_____--____-__--------__---_ 71 Origin.________________________________ 55 Garrison bank______-_______-___-______- 71 Deposits between residuum and older gravel Watson tract_________________________ 72 unit— _ ______________________________ 57 Fox Mountain mine.____________________ 73 Ancient gravel unit at Stanley mine.______ 57 Elkton mines_________-_-_____---_-_-- 74 Related deposits in other areas_'__________ 57 Seller mine__-___----_--------------_-_- 76 Age of residuum and of deposits between Ocher__________.___________________. 76 residuum and older gravel unit _________ -58 Mines___________________________________ 76 Gravel deposits_____________________________ 58 Stanley deposits-________-_-_--_----_--_ 76 Older gravel unit _______________________ 58 Naked Creek deposit_________-__-_-___-_ 77 Intermediate gravel unit.________________ 59 Limestone and dolomite-______________-_---_---_ 77 Younger gravel unit___________________ 60 Quarries. __________________________________ 77 Regional relations of gravel deposits______ 60 Elkton Lime & Stone Co. quarry________ 77 Origin and age of gravel deposits _________ 60 Quarries near Shenandoah _______________ 77 Relations between features of valley floor______ 62 Other quarries___----____-___--_-___--__ 77 Talus_______________________________________ 62 Building stone________________________________ 78 Character________________________________ 62 Copper and magnetite.__________________________ 78 Origin_____________________________________ 63 References cited.____________-_______-___-__--__--__ 78 Alluvium. _____________________________________ 63 Index.__-_-___-_-_---________---_---------_--_---- 81 TABLES Page Geological formations of the Elkton area________________________________-_-_-_---_-_----------__---------------- 6 Stratigraphic section of upper part of Tomstown dolomite near head of valley of Crooked Run__________________________ 26 Results of tests on dolomite from U. S. Bureau of Mines drill hole No. 2 on Watson tract__----------_-----------------_ 27 Results of tests on dolomite from U. S. Bureau of Mines drill hole No. 1 on tract south of Giants Grave_____------------- 27 Results of tests on dolomite from U. S. Bureau of