11. 



HUDSON VALLEY LAKE CHAMPLAIN REGION 



Relief Features 



The relief features of the Taconic erogenic system stretch along the 

 general Hudson Valley, Lake Champlain lowlands, and St. Lawrence 

 Valley. In addition to hills and ridges within the lowland, it is convenient 

 under this heading to discuss the Hudson highland and Catskill and 

 Adirondack Mountains on the west, the Laurentian highlands on the 

 northwest, and the Taconic and Green Mountains on the east. The 

 Taconic orogeny culminated in late Ordovician time, and most of the 

 structures of the Hudson and Lake Champlain valleys and of the ranges 

 along its eastern margin are Taconic. The Catskills and Adirondacks, 

 however, are part of the stable interior. See index map, Fig. 11.1 and 

 geologic map, Fig. 11.2. 



NEW ENGLAND 

 APPALACHIAN SYSTEMS 



DIVISIONS OF NEW ENGLAND APPALACHIANS 



The New England Appalachian systems will be divided for purposes of 

 discussion into a western belt and an eastern. The western belt includes 

 those structures in and on either side of the Hudson Valley and Lake 

 Champlain lowlands, and the eastern belt includes a north-south zone 

 through central and eastern Vermont, New Hampshire, and Maine. The 

 western zone is essentially the core of the Late Ordovician Taconic 

 orogeny and the eastern the site of the Late Devonian Acadian orogeny. 

 A third division may be recognized through Rhode Island and Massa- 

 chusetts on the far east where Carboniferous basins and related igneous 

 activity indicate a still later orogenic belt. 



Catskill Mountains 



The Catskill Mountains are west of the Hudson River and about 100 

 miles north of the city of New York. See geomorphic diagrams of Figs. 

 11.3 and 11.4. They are a dissected plateau with highest summit levels 

 about 5000 feet above sea level and local relief of over 3000 feet. They 

 were the site of pioneer geologic studies in North America, and in them 

 the stratigraphic sequence of the Silurian and Devonian systems was early 

 established. The Catskills proper consist of nearly flat-lying beds, gently 

 inclined toward the west, and as such are part of the Appalachian 

 Plateaus geomorphic province. The most widespread rocks are the 

 Devonian. Along the east margin and in the adjacent Hudson Valley, 

 the strata, especially the Cambrian and Ordovician, are highly deformed; 

 and the Devonian and Silurian beds rest on their beveled edges. The 

 classic angular unconformity between the Ordovician and Silurian beds, 

 which here marks the Taconic orogeny, is displayed along the southeast 

 margin of the Catskills. See the Geological Map of the United States. 

 Also, the system of folded and thrust-faulted Appalachians of the south 

 narrows here into a belt a few miles wide, and some of its late Paleozoic 

 structures may here be impressed on the strata and in part superposed 



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