Long thin packets of structurally disrupted rocks in the eastern core of the Olympic Mountains mostly top eastward, but the overall age of the rocks decreases westward, suggesting early folding around subhorizontal axes with imbricate thrusting or imbricate thrusting alone. Continued east-west compression overturned beds eastward, bending the packets into an arc within the horseshoe bend of the Crescent Formation, a foldlike structure that formed as the core rocks were imbricated or was extant from the original arcuate distribution of basaltic seamounts. In the western part of the eastern core, secondary structures (B elements) (mostly small-scale folds) developed parallel to the steep axis of the fold of the basaltic horseshoe; in the southern part of the core, the rock packets were sheared off beneath the basalts on the south limb of the horseshoe bend. Later shear folding on a cleavage fan oriented parallel to a north-northwesttrending subhorizontal kinematic axis rotated B elements (folds) formed earlier, producing widespread late pencil structures, in part centripetal to the basaltic horseshoe, where the late cleavage intersected earlier deformed bedding and cleavage. This late folding produced a domelike structure extended asymmetrically eastward. The complex structure of the core rocks is consistent with current models of accretionary prisms in subduction zones and developed its form as the thick mass of volcanic rocks ofthe Crescent Formation to the east resisted the eastward movement of the accreted sedimentary prism.

Introduction Acknowledgments • 517 Previous work 519 Stratigraphy • 524 The present classification Lower Cambrian series General correlation Formations Distribution and genetic relations Upper Cambrian series 53,4 General correlation Formations Distribution and genetic relations Ordovician-Beekmantown "group" General correlation Formations Distribution and genetic relations Ordovician-Chazy group General correlation Formations , Distribution and genetic relations Ordovician-Black River group General correlation and Uthology Distribution and genetic relations Ordovician-Trenton group General correlation Formations Distribution and genetic relations Succeeding groups Structural geology Major structures General setting 562 Synclinoria Anticlinoria Thrust faults '. 564 Normal fault system 570 Lesser structures 572 General relations Detailed description 572 Summary statement 575 Structural details 575 General scope 575 515 516 W. M. CADY-STRATIGRAPHY AND STRUCTURE OF WEST-CENTRAL VERMONT Foliation 575 Flow structure 575 Flexures 576 Ruptures 576 Mechanism of deformation 577 Diastrophic relations General statement 579 Taconic Allochthone 579 Foreland thrusts and associated folds 580 Adirondack normal faults 580 References cited 581 ILLUSTRATIONS Figure Page 1. Geographic location of west-central Vermont 518 2. Wing's manuscript sketch map, and cross sections of Middlebury synclinorium 520 3. Stratigraphic correlation of west-central Vermont and adjoining areas 522 4. Columnar sections of strata in west-central Vermont 527 5. Regional geologic map 563 6. Palinspastic map of the region of western New England, eastern New York, and southern Quebec 568 Plate Facing page 1. Major topographic features 515 2. Lower Cambrian strata 526 3. Upper Cambrian and Beekmantown strata 527 4. Chazy strata 548 5. Trenton strata 549 6. Major structures 562 7. Cleavage-bedding relations 563 8. Flow structure 576 9. Folds 577 10. Areal geology and structure of west-central Vermont ;.. In pocket ABSTRACT The lithologic units recognizable in the fossiliferous succession along southern Lake Champlain are structurally continuous with and traceable eastward into the "marble belt" of west-central Vermont immediately west of the Green Mountain Front. They are also traceable northward through west-central Vermont into a succession in northwestern Vermont bounded on the east and west by major thrusts, where they pass laterally northeastward into fossiliferous shales, the faunal zones of which are correlated with those along southern Lake Champlain and in the Hudson and Mohawk valleys. The Cambrian strata are traced into west-central from northwestern Vermont whereas the Ordovician correlation is with rocks in the Mohawk-Hudson-Champlain region. Certain of the Upper Cambrian strata can be correlated with established formations of this age in both of the outlying areas. The structural pattern reflects movements dependent upon the original distribution of sedimentary facies. Interbedded Carnbro-Ordovician limestones and dolomites grade westward into fo...

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