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Published May 1950 | Published
Journal Article Open

Structure of Central and East-Central Vermont

Abstract

The formations of central and east-central Vermont are exposed as a series of parallel belts that strike nearly north. Most of the rocks dip steeply, and many are overturned. With one possible exception, there seem to be no major repetitions within the sequence, and the order of formations from west to east appears to be the same as the order of their deposition. The formations are dominantly schist or phyllite, with varying proportions of arenaceous material. One thin formation, the Shaw Mountain, contains quartz conglomerate, calcareous tuff, and crinoidal limestone. The third-from-highest formation, the Waits River, is very thick and contains a large proportion of calcareous beds. The distance from the base of the lowest formation to the top of the highest, measured normal to bedding, is more than 100,000 feet; this large apparent thickness is believed to be not very much greater than the original thickness. The metasediments have been intruded by granitic dikes and plutons, mafic dikes, and small ultramafic plutons. Two principal stages of deformation are distinguished. During the earlier stage the rocks were folded, and a schistosity was developed nearly parallel to bedding. Throughout the area the minor folds of this stage indicate a consistent upward movement of rocks on the east with respect to those on the west. The folds plunge at low to moderately steep angles, typically northward. Phenomena associated with the later stage of deformation decrease in intensity both eastward and westward from the belt underlain by the calcareous Waits River formation. At a distance from this formation, the rocks have prominent slip cleavage, and the earlier schistosity is folded. The minor folds plunge moderately to steeply northward on the western side of the area and more gently northward on the eastern. As the Waits River formation is approached, slip cleavage passes gradually into a schistosity that obliterates the earlier schistosity, and the intensity of later folding increases. In both the eastern and the western parts of the area the later minor folds indicate that the rocks of the Waits River formation have moved upward with respect to the formations on either side. The central part of the belt underlain by the Waits River formation is marked by a huge arch, 10-20 miles across, whose axis is more or less parallel to the belt and plunges gently northward. This is shown to be an arch, not in bedding, but in the later schistosity and in the axial planes of large isoclinal folds that were formed during the later stage of deformation. The axial planes of three of these large isoclinal folds can be correlated across the crest of the cleavage arch at Strafford Village.

Additional Information

© 1950 University of Chicago Press. The writers are indebted to Jarvis B. Hadley, of the U.S. Geological Survey, who has generously permitted the use of his unpublished maps of the Vermont part of the Mount Cube quadrangle. They have profited throughout the period of investigations from discussions with Hadley, L. W. Currier, and R. S. Cannon, Jr., of the Geological Survey, and with M. P. Billings, of Harvard University. White gratefully acknowledges the capable work of J. H. Eric, Edgar Breed, Richard H. Story, and Ralph Hornblower, Jr., each of whom spent a summer as a field assistant in the Woodsville quadrangle. Eric and T. W. Amsden also did much of the subsequent geologic mapping in the Orange County copper district. Most of the illustrations were drafted by Joan T. Rounds, of the California Institute of Technology. Considerable improvement in the manuscript resulted from the careful criticism of W. M. Cady, J. B. Hadley, and P. B. King, of the Geological Survey.

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Created:
August 21, 2023
Modified:
October 23, 2023