CONTENTS vii 



PAGE 



Tuckernuck . . . 112 



Muskeget .112 



Bibliography of the geology of Nantucket . . . . . . . .114 



Chapter II. — Geology of Marthas Vineyard, by Edward Wigglesworth, with notes by 



J. B. Woodworth 117 



Geography 117 



General features 117 



Topographic divisions . . . . 118 



The western area ........... 118 



The northeastern area . . .119 



The great plain 119 



Notable topographic features . . . . . . . .119 



Geologic significance of the topography . . . . . . . 120 



Salient geologic features . . 121 



Effects of the Wisconsin ice sheet .122 



Form of the island ........... 123 



Influence of the older topography .124 



The Buzzards Bay lobe of the ice sheet ...... 124 



The Cape Cod Bay lobe . . . 125 



Moraines 126 



Stratified moraines 126 



Till moraines ........... 126 



Kettles . . . . 127 



Older valleys . 127 



Outwash features . 129 



The outwash plain 129 



Ice contacts . . . . . 129 



Kettles 131 



Channels ........... 132 



Shore features . . . 132 



Constructive action 133 



Destructive action 134 



Landslides 136 



Stratigraphic geology 136 



Introduction 136 



Difficulties of mapping 136 



Nature of the deposits ......... 136 



The topographic map ......... 136 



The Wisconsin drift 136 



Sections in the cliffs . 137 



Sections in the interior 137 



Lithological similarity of the Pleistocene deposits . . . . 137 



Lack of borings 138 



Nature and age of the pre-Pleistocene deposits ..... 138 



Nature and age of the Pleistocene deposits ....... 139 



Probable nature and depth of the pre-Cretaceous basement . . . 139 



Cretaceous system 140 



Names of the beds ... ........ 140 



Subdivisions 140 



