170 



STRUCTURAL GEOLOGY OF NORTH AMERICA 





NORTHWESTERN 

 VERMONT 



Montpelier Quad. 

 Cady, 1956 



CENTRAL AND EAST 

 CENTRAL VERMONT 



White and Jahns, 1950 



WESTERN, CENTRAL 



AND NORTHERN 



NEW HAMPSHIRE 



Billings, 1956 



SOUTHEASTERN 

 NEW HAMPSHIRE 



Billings, 1956 



LOWER 

 DEVONIAN 



SILURIAN 





?Meeting House slate 

 Gile Mountain fm. 



Littleton fm. 

 15,000'+ 



Littleton fm. 



15,000'± 



Waits River fin. 

 Northfield slate 



"Standi fig Pond vols. 

 Waits River fm. 



Northfield slate 



Fitch, fm. 

 0-769' 



Berwick fm. 

 10,000'+ 



Eliot fm. 

 6,500'i 



ORDOVICIAN 



Shaw Mtn. fm. 



Serpentine, talc- 

 carbonate rock, 

 and steatite 



Shaw Mountain fm. 

 Ultramafic rocks 



Clough quartzite 

 0-1200' 



Partridge fm. 

 0-2000' 



Ammonoosuc vols. 

 2000-5000' 



Kittery quartzite 

 1,500'± 



Rye fm. 



2,000'i 



Moretown fm. 

 Stowe fm. 



Cram Hill fm. 



Arenites of the Brain- 

 tree-Northf ield Range 



Albee fm. 

 5000' 



Orfordville fm. 

 3500-4000' 





CAMBRIAN 



Ottauquechee fm. 

 Camels Hump gr. 



Ottauquechee phyllite 



Pinney Hollow schist 



Quartzose schist, 

 quartzite, dolomite, 

 and conglomerate 





PRECAMBRIAN 



(To the southwest) 





Fig. 11.18. Correlation chart of pre-Acadian Paleozoic formations across Vermont and New 

 Hampshire. The Standing Pond volcanics and Meeting House slate are listed by Billings for 

 westernmost New Hampshire in the stratigraphic order shown but not included by Cady for 

 Vermont. The total Vermont section is immensely thick. 



Ordovician time, another uplift, the Oswegan disturbance, occurred and 

 spread westward past the Adirondack axis into the Allegheny basin. 



Taconic Orogeny. At the close of the Ordovician period the major 

 Taconic orogeny occurred, and the argillaceous rocks of the Magog trough 

 were thrust far westward. The Quebec barrier and eastern part of the 

 Champlain trough were concealed by it. The amount of horizontal dis- 

 placement probably exceeded 40 miles (Kay, 1942). 



The thrust sediments are in tectonic contact on Queenston shale in south- 

 eastern Quebec, and the autochthonous Cincinnatian has been folded con- 

 siderably. The overthrust rocks are overlain at Becraft Mountain, New York, 

 and in the Catskill Front by latest Silurian Manlius limestone. Thus, there is 

 direct evidence that the principal lateral movements were pre-Manlius and 

 post-Queenston. Folds in autochthonous Ordovician are truncated by the 



Shawangunk and Tuscarora quartzites of the earliest Silurian in southeastern 

 New York and Pennsylvania; if the folding accompanied Taconic thrusting, the 

 revolution is pre-Silurian. 



The front of the thrust sheet is not very high. Middle Ordovician sediments 

 are preserved near to the westernmost remnant of the sheet and probably never 

 were buried deeply. On Anticosti Island in the Gulf of St. Lawrence, there is 

 essentially continuous section of Cincinnatian and early Silurian calcareous shale 

 and limestone in the Champlain belt within 50 miles of the overthrust rocks 

 of Gaspe; the allochthone was beneath the sea or not high enough to produce 

 significant detritus after the revolution. Though the quantity of Silurian terrig- 

 enous sediments is distinctly smaller than that of the Ordovician, . . . this 

 reflects repeated uplift and continued presence of Vermontian highlands in 

 later Ordovician, in contrast to progressive reduction of the transposed Taconia 

 in the Silurian. The greatest quantity of eroded material was laid down in the 

 latitude of Pennsylvania, as shown by isopachs; that the greatest elevation was 

 there is also shown by the coarser texture of the sediments. The lateral move- 

 ment of the allochthone may have been as great or even greater in Quebec, but 

 Vermontia and its transposed descendant, Taconia, were more continually high 

 farther south. 



Acadian Orogeny. The next great influx of clastic sediments was in the 

 Middle Devonian, and the sediments generally coarsen upward and east- j 

 ward. They came from rising highlands on the east. The elevation termi- 

 nated in the Acadian orogeny which was followed by the deposition of " 

 Mississippian elastics to the west of the orogenic belt. 



The Acadian belt is known best in New Hampshire and the Maritime 

 Provinces and will be described later, but it is possible that it spread 

 westward to the Hudson Valley and Lake Champlain lowlands and im- 

 pressed additional folds on the Taconic structures. It is possible, also, 

 that the later structures are Appalachian in age. 



Unsolved Problems. The above summary of the history of the Taconic 

 system savors of those who postulate the great Taconic allochthone, and 

 this is the general opinion of those who have worked in northern Massa- 

 chusetts, Vermont, and eastern New York. Yet Balk and Craddock in very 

 thorough work, at the south end of the Taconic klippe where the great 

 thrust and its roots should be found, do not find evidence of it, and 

 they do not believe the thrust theory necessary to explain the facies and 

 metamorphism there. Similarly, the roots of the thrust are not yet estab- 

 lished at all well in the Green Mountains. 



