Slope movements in the Lower Cambrian Cheshire Quartzite of the western Green Mountains in Vermont are characterized by block slides, rock falls, and more rarely, by toppling failures. Slides and falls occur on steep hillslopes underlain by massive quartzite, whereas topples are unique to thin-bedded, tectonically deformed quartzite containing interbeds of graphitic schist. Freeze-thaw mechanisms dominate displacements of massive blocks, while rainfall induces toppling displacements. Movement of massive blocks occurs primarily in early spring and late fall. Bedrock discontinuities, including microfractures, joints, and bedding surfaces, are of primary importance in facilitating initial slope breakup and in controlling the subsequent mode of downslope rock-mass movement. The results of investigations at three sites in the Cheshire-Quartzite show that movement rates are controlled by structural conditions and slope-development patterns. A typical freeze cycle during testing of a physical block model in the laboratory produced a displacement of 0.13 mm, which agrees reasonably well with the 0.26 mm annual displacements measured at two cliff-edge blocks at a rock-fall site. Gravity-induced toppling movements in much less massive quartzite are more rapid.

In southwestern Connecticut and southeastern New York, a sequence of Precambrian rocks is unconformably overlain by a Cambrian-Ordovician quartzite-carbonate sequence. This, in turn, is unconformably overlain by a dark-gray fissile sillimanite schist that locally has calcite marble and calcite-rich mica schist at its base. The Paleozoic portion of this stratigraphic sequence correlates with the miogeosynclinal sequence of eastern New York and the western parts of Vermont, Massachusetts, and Connecticut. A eugeosynclinal sequence is in contact with the fissile schist of the miogeosynclinal sequence. This eugeosynclinal sequence consists of the following rock units in order eastward from the fissile schist and apparently in order from oldest to youngest: (1) feldspathic garnet-muscovite-biotite schist commonly with sillimanite nodules and with some interbedded amphibolite; (2) garnet-muscovite-biotite schist with local sillimanite and (or) kyanite, amphibolite, and light-gray or white biotite-muscovite-quartz-feldspar gneiss locally containing garnet; (3) white biotite-muscovite-quartz-feldspar gneiss locally containing garnet; (4) interbedded garnet-muscovite-biotite-quartz-feldspar schist and muscovite-biotite-quartz-feldspar granulite; (5) dark-gray biotite- and (or) hornblende-quartz-feldspar gneiss with feldspar augen common. A suggested correlation of these units with formations in Connecticut and Massachusetts is as follows: (1) correlates with the Waramaug and Hoosac Formations; (2) and (3) with part of the Hartland Formation, Rowe Schist, and the Trap Falls Formation; (4) with parts of the Hartland, Taine Mountain, Moretown, and Fairfield Formations and the banded schist member of the Southington Mountain Formation; and (5) with parts of the Prospect, Collinsville, and Hawley Formations. If the above correlation is correct, the eugeosynclinal sequence in southwestern Connecticut is the same age as the Cambrian-Ordovician miogeosynclinal sequence, and its structural position above the miogeosynclinal sequence can be explained by a major premetamorphic thrust fault similar to, if not actually, the Taconic thrust fault. The proposed correlation also suggests that Silurian rocks rest unconformably on overturned pre-Silurian rocks in the vicinity of the Westport, Bridgeport, and Long Hill quadrangles in southern Connecticut.

In recent years, a rapidly expanding database, especially in sensitive high-resolution ion microprobe (SHRIMP) geochronology, has led to significant advances in understanding of the Precambrian tectonic evolution of the Grenville Province, including its Adirondack outlier, and the Mesoproterozoic inliers of the Appalachians. Based upon this information, we review the geochronology and tectonic evolution of these regions and significant similarities and differences between them. Isotopic data, including Pb isotopic mapping, suggest that a complex belt of marginal arcs and orogens existed from Labrador through the Adirondacks, the midcontinent, and into the southwest during the interval ca. 1.8–1.3 Ga. Other data indicate that Mesoproterozoic inliers of the Appalachians, extending from Vermont to at least as far south as the New Jersey Highlands, are, in part, similar in composition and age to rocks in the southwestern Grenville Province. Mesoproterozoic inliers of the Appalachian Blue Ridge likewise contain some lithologies similar to northern terranes but exhibit Nd and Pb isotopic characteristics suggesting non-Laurentian, and perhaps Amazonian, affinities. Models invoking an oblique collision of eastern Laurentia with Amazonia are consistent with paleomagnetic results, and collision is inferred to have begun at ca. 1.2 Ga. The collision resulted in both the ca. 1190–1140 Ma Shawinigan orogeny and the ca. 1090–980 Ma Grenvillian orogeny, which are well represented in the Appalachians. Several investigators have proposed that some Amazonian Mesoproterozoic crust may have been tectonically transferred to Laurentia at ca. 1.2 Ga. Data that potentially support or contradict this model are presented.

The Boundary Mountains terrane is defined primarily by a sialic basement consisting of a distinctive suite of diamictites, which were metamorphosed in late Precambrian time to granofels, gneiss, and schist. These rocks make up the Chain Lakes massif, exposed in the Boundary Mountains along the southwestern part of the Maine–Québec border, and large blocks of similar lithology exposed in mélange of the St. Daniel Formation, Eastern Townships of Québec. Rocks of similar lithology and age stand out as megaclasts in ophiolitic mélange near the northwest margin of the Macquereau dome, southeastern Gaspé Peninsula. The cratonal basement of the Boundary Mountains terrane may extend from central or northern New Hampshire and northeastern Vermont roughly 1,000 km to the western part of the Gulf of St. Lawrence, southeast of Gaspé. Collectively, these basement rocks are unlike those composing the Grenville tectonic province of the Laurentian Shield, and unlike high-grade gneisses exposed in the Miramichi Highlands of New Brunswick and in lithotectonic assemblages of Avalonian aspect bordering the Gulf of Maine and the Bay of Fundy. The accretionary history of the Boundary Mountains terrane is believed to have begun in Middle to Late Cambrian time. It therefore may represent one of the earliest of accretionary events in the prolonged orogenic history of the northern Appalachians. Two parallel mélange belts, the Hurricane Mountain and St. Daniel, of the Maine and Québec portions, respectively, of the northern Appalachians, are interpreted as suture zones that define the southeast and northwest margins of the Boundary Mountains Terrane. They are named for the predominant lithotectonic units in each belt—the Hurricane Mountain Formation, in the Lobster Mountain anticlinorium of Maine, and the St. Daniel Formation, which crops out along the southeast margin of the Baie Verte–Brompton line in Québec. The tectonic history of the Hurricane Mountain mélange belt is interpreted as expressing the amalgamation, during Late Cambrian to Early Ordovician time, of the Boundary Mountains terrane to a second terrane on its southeastern margin, probably the Gander. Sparse paleontologic and isotopic ages along the Hurricane Mountain belt indicate that suturing progressed from present-day southwest to northeast, along an ensimatic convergent plate boundary. Volcanogenic flysch deposits of the Dead River Formation, overlying the Hurricane Mountain Formation to the southeast, are believed to have formed in a forearc-basin environment. Polarity of subduction is inferred to have been toward present-day southeast. This diachronous event provides a tectonic driving mechanism, in time and space, for the Penobscottian orogeny. The Penobscottian event preceded the Taconian collision of the composite Boundary Mountains–Gander terrane to the Laurentian (North American) margin. Amalgamation of individual terranes, therefore, in this part of the northern Appalachians, did not proceed in a regular, craton-outward succession.

Abstract Most of the stratigraphic section of New York, ranging from Cambrian to Lower Pennsylvanian, forms a southward-thickening wedge into the Appalachian geosyncline. Oil and gas production is primarily from the Devonian and Silurian Systems. Oil production is obtained from the Upper Devonian in the southern tier of counties adjacent to Pennsylvania. Gas production is primarily from the Oriskany and Medina sandstones in central and western New York. The Trenton Limestone (Ordovician) has produced minor amounts of gas. Future prospects, listed by geologic age, are (1) the Oriskany in southwestern and central New York, (2) possible Middle Silurian- reefs along the northern edge of the Silurian salt basin, and (3) the Cambrian-Ordovi- cian of central and western New York. Three geographic areas are prospective: (1) offshore Lake Erie for objectives from the basal Onondaga to the basement, (2) the central part of the state for Lower Silurian and Upper Ordovician objectives, and (3) the folded Allegheny synclinorium adjacent to Vermont.