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The Great V alley (fJhenandoah V alley) o f e a s te r n West V irg in ia i s the northern extension o f the Shenandoah Valley of V irginia and marks th e e a s te r n l i m i t o f th e V alley and Ridge p h y sio g rap h ic p ro v in c e . The valley is underlain by non resistan t carbonate rocks and shales of Cambrian and Ordovician age which have been eroded to produce a r e la ­ tiv e ly f la t to ro llin g te rra in . The s u rfa c e geology o f th e G reat V alley i s dominated by the n o rth - n o r th e a s t tre n d in g M assanutten sy n c lin o riu m . The a x is o f t h i s s t r u c t u r e coincides with a b e lt o f Martinsburg Shale west of the center o f the v a lle y . The w estern limb o f th e Massanutten synclinorium i s in f a u lt contact with the Silurian-D evonian formations of North Mountain, Near the Blue Ridge the eastern limb o f the synclinorium is coincident with the w estern, overturned flank o f the South Mountain anticlinorium . Folds superimposed upon the b asic stru c tu re o f the synclinorium are asymmetric to the west and overturned to a near-recumbent p osition a t many p la c e s n ear th e Blue Ridge; cleavage dips g e n tly eastw ard in a fan arrangement. Progressively westward the ax ial planes o f folds become more s te e p ly in c lin e d , and in th e w estern b e l t o f th e v a lle y folds are generally symmetrical with v e rtic a l cleavage fans, High-angle and low-angle lo n g itu d in a l fa u lts are present in the cen tral and western p arts of the valley but are, as y et, undetected in the eastern p a rt o f the valley, High-angle transverse fa u lts are common throughout th e v a lle y , A p ro g re s s iv e decre ase o f g r a v ity v alu es t o th e west from th e v i c i n i t y o f th e B altim ore dome su g g ests t h a t g r a v ity s l i d i n g was inv o lv ed in th e deform ation o f th e Blue Ridge and G reat V a lle y , The uniform ity of the gravity gradient and the sim ila r d e n sitie s (approximately 2,70) o f the g ran itic gneiss basement and the younger sedimentary rocks in d ic a te th a t folds have no "ro o ts" in th e sim atic la y e r o f the basement. D eformation o f th e rocks o f th e G reat V alley and Blue Ridge was the r e s u lt of the Appalachian Revolution and probably occurred in four major phases, Intensive folding with attendant cleavage development marked the f i r s t phase. Thrust fa u lts and high-angle, lo n g itu d in a l, reverse fa u lts characterized the second phase. Transverse shear fa u lts developed and o ffs e t previous stru ctu re s during the th ird phase. Deformation ended a f te r a fourth, or "relax atio n ", phase which is represented by longitudinal and transverse normal fa u lts .