158 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



Fig. 11.5. Cross section along the Catskill aqueduct. Reproduced from Geological Society of America 

 Guidebook of Excursions, 1948. 



areas to this time. The distribution of faults and the Taconic front are 

 shown in Fig. 11.12 in relation to the Lower Ordovician facies. 



Lower Hudson Valley Crystallines 



Definition. The block diagrams of Figs. 7.3 and 11.3 show the lower 

 Hudson Valley area to be made up of the Triassic basin sediments and 

 sills, and the New England upland. The following paragraphs concern 

 the New England upland thus designated, but the term is general for 

 much of New England, and more specific names have been given to the 

 features of the lower Hudson Valley area. The Reading prong of Penn- 

 sylvania and the New Jersey highland merge on the northeast with the 

 Hudson highland, whose upland surface is about 1000 feet above sea 

 level. The Hudson River cuts a fairly narrow valley without flood plain 

 through the highland between Newburgh and Peekskill. See map of Fig. 

 11.3. The Hudson highland continues northeastward into Connecticut as 

 the Housatonic highland. 



Lower Hudson Valley. From Peekskill to Manhattan Island, the Hud- 

 son is bounded on the west by the Triassic rocks, mostly thick diabase sills 

 that form the Palisades of the Hudson, and on the east by rounded hills 

 of a metamorphic and plutonic complex. The rocks along the route from 

 New York City to Peekskill consist of gneisses intruded and injected by 

 granite with infolded belts of limestone and schist. See cross section of 

 Fig. 11.8. The major structural axes trend north-northeast and are strongly 

 reflected in the general arrangement of ridges and valleys. Along the 

 lower part of the river in the vicinity of Yonkers, the structures trend 

 about N. 20° E. and are parallel with the river, but a few miles above 



Yonkers they strike more easterly, whereas the course of the river is nearly 

 due north. 



Hudson and Housatonic Highlands. Balk (1937) and Barth (1937) 

 have made a thorough study of the Hudson and Housatonic highlands 

 and adjacent areas, and report a complex of Precambrian crystalline 

 rocks and a series of three sedimentary formations of Cambrian and 

 Ordovician age. The highlands themselves are formed of a complex of 

 gneisses of granitic and syenitic composition. Associated are injection 

 gneisses as well as narrow tracts of amphibolite, marble, and other highly 

 metamorphic rocks. Along the northwestern border of the highlands, 

 medium- to coarse-grained granites and granite gneisses are fairly abun- 

 dant. 



The Paleozoic strata are described by Balk (1937) as follows: 



The oldest Paleozoic rock is a pink or white quartzite (Poughquag quartzite) 

 that rests unconformably upon the various pre-Cambrian rocks. At the base, a 

 conglomerate may be present, though rarely more than a few feet thick. Quartz 

 pebbles, about an inch across, and an occasional black chert fragment, are the 

 most abundant constituents. Fossils of Lower Cambrian age have been described 

 from several localities in southeastern New York. 



The quartzite is succeeded by a sequence of carbonate rocks to which, in 

 the Poughkeepsie area, the name, Wappinger terrane, has been applied. As 

 elsewhere in the Appalachian region, the rocks include members of Cambrian 

 and Ordovician age, but Quaternary deposits obscure so much of the bedrock 

 that no complete section is available. Fossils ranging from Lower Cambrian 

 to Middle Ordovician have been reported from various localities, but it is 

 believed that there are several disconformities within the terrane. The thickness 

 of the series is difficult to estimate, but may well exceed 1,000 feet. 



A series of slates and similar rocks, resting on the carbonate rocks, is called 

 the Hudson River pelite. Fossils of Middle Ordovician age have been found in 



