Comparisons of the 2005 Geologic Map of North America with the 1965 Map, Areas 1-4
4. Eastern and central United States and parts of southern Canada
- In the northern part of this view the refinements in the geology of the Precambrian rocks of the Canadian Shield (A), the Adirondacks (B), and eastern Wisconsin (C) on the new map are conspicuous.
- In the central interior region there is relatively little difference between the old and new maps. Mississippian and Pennsylvanian strata have been further subdivided in the Michigan (D) and Appalachian (E) Basins, and Jurassic rocks in the Michigan Basin have been shown. Special features such as impact structures, alkaline igneous complexes, and limits of continental glaciers have been added and some contacts more accurately placed, but the changes and additions are relatively minor.
- In the Valley and Ridge province of the southern Appalachians (F) the general distribution of rock units is very similar, but the new map shows many more thrust faults. In the Taconic Province in western New England and eastern New York (G) several extensive and tectonically important thrust faults have been added.
- In the Piedmont of the Southern Appalachians (H) and in central and eastern New England (I) granitic plutons, all shown as Paleozoic on the 1965 map, are subdivided into Late Proterozoic and Cambrian plutons, Cambrian and Ordovician plutons, Silurian and Devonian plutons, and Mississippian and Pennsylvanian plutons. Granite plutons of the White Mountains in New Hampshire, shown as Paleozoic on the 1965 map, are now known to be Triassic and are shown as such on the new map. The extensive swarm of Mesozoic diabase dikes in the Piedmont has also been added to the new map.
- Cretaceous and Tertiary sedimentary rocks of the Atlantic Coastal Plain (J) have been more fully subdivided and their relation to rocks of similar ages on the Atlantic Continental Shelf (K) and Rise (L) are portrayed. Slump structures, submarine canyons, and other marine features on the shelf and rise are also shown, as are major impact structures in Chesapeake Bay and on the shelf southeast of New York City.
Return to comparisons of map areas 1-4.
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