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A 150-km-Iong seismic line was shot from a point on the St. Lawrence River 50 km southwest of Quebec City, southeastward to the U.S. border in 1979. The line crosses the autochthonous domain, the foreland thrust belt, and the allochthonous domain of the Humber Zone; it also crosses the Dunnage Zone and overlying rocks of the Connecticut Valley-Gaspe synclinorium. Reflectors on the derived seismic profile have been correlated with surface geology and the logs of four deep wells, and in turn used to construct a deep structural profile across the Appalachians of southern Quebec. The principal conclusions drawn from the profile are: (A) Grenville basement occurs at depth under the Humber Zone, and along with cover rocks, it has been cut by southeast-dipping syndepositional normal faults in the authochthonous domain, the foreland thrust belt, and the northwestern part of the allochthonous domain. Several of the fault blocks were tilted northward. (B) Nappe emplacement took place during Middle Ordovician time. (C) Later Acadian(?) thrust faults in the Notre Dame anticlinorium may have utilized progressively deeper levels of detachment and at depth may involve Grenville basement. (D) Rocks of the Connecticut Valley-Gaspe synclinorium have been thrust over the Dunnage Zone, and along the seismic line they contain no granite plutons at depth. 103

In Ecuador and northwestern Peru the Andes and adjacent country, particularly on the Pacific side, are composed of at least five distinctive geologic terranes. The terranes are distinguished from one another and from cratonic South America to the east by dissimilar basements, cover rocks, intrusive rocks, and Bouguer gravity anomaly fields.The Piñón terrane, occupying most of coastal Ecuador, has a basaltic basement characterized by the largest known on-land positive Bouguer anomalies in the western hemisphere. The Tahuín terrane occupies most of northwestern Peru and the southwestern corner of Ecuador. The terrane has an especially complex basement and is the site of generally positive Bouguer anomalies. The small Birón terrane has an unusual basement composed in part of cordierite gneiss and amphibolite that give consistent Late Cretaceous K – Ar mineral ages. The wedge-shaped Chaucha terrane lies in part on the western Andean slope, between the oceanic Piñón terrane on the north and the continental Birón terrane on the south. The vast Santiago terrane composes the high Andes of southern Ecuador and northwestern Peru. It is the site of the unique Santiago Formation, a thick succession of Lower Jurassic limestones found nowhere else in the region.Geologic and geophysical evidence supports the view that the five terranes are parautochthonous or allochthonous fragments emplaced against cratonic South America from Middle Jurassic to Late Eocene time. Continental-border subduction alone (at the so-called "Andean margin") may have been an inadequate engine for orogeny. Additional allochthonous terranes perhaps await identification at other places along the Andes. Whether the emplacement of allochthonous terranes has been an important process elsewhere in the tectonic development of the Andes remains to be established. Geologic mapping on the oceanward western border of the Andean orogen, studies of basement petrology and chronology, and paleomagnetic studies are particularly needed.The distribution of mineral deposits (including petroleum) in Ecuador and northwestern Peru is not uniform but is instead related spatially to the five terranes and cratonic South America. This relationship can be useful to prospectors.