MARITIME APPALACHIANS 



199 



same general area is a broad belt of Upper Ordovician conglomerate and 

 grit about 2000 feet thick. Its relations to underlying beds are not noted. 



The Arisaig Silurian series of Nova Scotia contains conglomerates and 

 rests on Lower Ordovician volcanics. At Oak Bay in southern New Bruns- 

 wick, the base of the Silurian succession is a coarse conglomerate which 

 rests unconformably on the dark argillite of Ordovician age. 



Lower Devonian red slates and gray sandstones southwest of Arisaig 

 overlie with a marked unconformity Silurian strata. Arkoses and con- 

 glomerates occur in the Lower Devonian of Cape Breton Island. Much of 

 the interior of the Gaspe Peninsula is underlain by Middle Devonian 

 sandstones, conglomerates, and arenaceous shales. The change from lime- 

 stones of the Lower Devonian to elastics of the Middle Devonian is gen- 

 erally regarded here as marking the principal phase of the Acadian 

 orogeny. In the zinc and lead district of Berry Mountain and Brandy 

 Brooks, the limestones are cut and mineralized by granitic and syenitic 

 intrusive rocks, but not the overlying sandstones. 



Upper Devonian beds on the north side of Chaleur Bay consist at 

 the base of about 600 feet of coarse conglomerates and sandstone. These 

 have been cast into a broad syncline, eroded, and are unconformably 

 overlain by the Pennsylvanian Bonaventure conglomerate. More con- 

 glomerates of the Late Devonian age occur in New Brunswick near 

 the Maine border; they are correlated with the Perry conglomerate of 

 Maine. These beds are seen to rest unconformably on the Silurian rocks, 

 and they contain boulders of the Silurian and pre-Silurian rocks of the 

 St. George granitic intrusives. 



The Carboniferous sediments rest everywhere, it is believed, in marked 

 angular unconformity on older rocks, which range from Precambrian 

 to Late Devonian in age. They are thousands of feet thick and contain 

 great quantities of coarse elastics, particularly the Pennsylvanian. In 

 Nova Scotia, the Horton Bluff elastics at the base of the Mississippian 

 rest unconformably on pre-Carboniferous metamorphics and igneous 

 rocks, and are in turn separated by an angular unconformity from the 

 overlying Cheverie, also of Mississippian age. 



Mississippian limestones and volcanics are folded, eroded, and over- 

 lain unconformably by Pennsylvanian (?) strata on the Magdalen Islands. 



Gussow's (1953) studies in New Brunswick lead to the conclusion that 

 the Lower Mississippian strata rest unconformably on the older Acadian 

 complex, and in turn are overlain unconformably by the Upper Missis- 

 sippian strata. The Upper Mississippian strata were in turn strongly 

 folded and faulted, eroded, and overlain unconformably by the Penn- 

 sylvanian elastics. The structure imposed on the Mississippian strata, 

 both during and at the close of the period, is typically Appalachian-type 

 folding and thrust faulting. The Pennsylvanian strata have not been dis- 

 turbed to any extent since deposition and are essentially flat. The great 

 amount of conglomerate attests the vigorous elevation of sizable high- 

 lands immediately before and during deposition. 



Folds and Thrusts 



All pre-Carboniferous rocks are considerably deformed and in part 

 metamorphosed. In places, the Carboniferous strata are also deformed. 

 The chief structures are folds. Some thrusts have been observed and 

 mapped, particularly in New Brunswick, but for the most part mapping 

 has not been sufficiently detailed to bring out the existence of long and 

 great thrust sheets. The linear elements in the compressional structures 

 trend generally northeastward in continuation of those of New England. 

 The folds and thrusts of the Taconic and Acadian systems of New York 

 and Vermont pass into southern Quebec, and the Taconic front reaches 

 the St. Lawrence at Quebec City. There the Quebec formation carries 

 Trenton fossils, and consists of limestone and shale and thin beds of lime- 

 stone conglomerate. See Fig. 12.6. Its beds have been altered and cleaved. 

 Beds of the older Levis formation have been thrust from the southeast 

 against the Quebec City, whereas on the northeast the Quebec City is 

 thrust against and over younger Upper Ordovician beds, the Utica- 

 Lorraine. The Utica-Lorraine in turn is in contact with the Precambrian 

 of the Canadian Shield. Resting horizontally and free from disturbance, 

 directly on the Precambrian, are Trenton limestones unlike the beds of 

 the Quebec City formation of similar age. This boundary between the 

 highly deformed and the undeformed strata has long been known as 

 Logan's line or Logan's fault (see map, Fig. 12.2). From Quebec City 

 the line runs under the waters of the St. Lawrence, and sweeps in a 



