faulted contact with rocks of the Laurentian shelf and slope-rise in the southern Appalachians suggest they were built on the margin of Laurentia, beyond the edge of the continental shelf-slope break. In the southern Appalachians, the Ordovician Laurentian margin probably resembled that seen in the modern Sea of Japan, with the continental mainland separated from a volcanic arc by a narrow, "marginal" seaway. Other lines of evidence supporting a back-arc, Sea of Japan-style tectonic model for the Taconic orogeny in the southern Appalachians include mixing of Ordovician and Grenville (ca. 1 billion year old) detrital zircons in metamorphosed sedimentary sequences, and interlayering of metamorphosed Ordovician volcanic rocks with sedimentary rocks derived from the Laurentian margin. Relation with the Famatinian orogeny It has been suggested that the coeval Famatinian orogeny in Western Gondwana (South America) is the "southward" continuation of the Taconic orogeny. This has been explained by adding that the continent Laurentia could have collided with Western Gondwana in early Paleozoic times due to the closure of the Iapetus Ocean. According to this view the Cuyania terrane would be an allochtonous block of Laurentian origin that was left in Gondwana. But such views are not unchallenged since Cuyania is alternatively suggested to have drifted across Iapetus Ocean as a microcontinent starting in Laurentia and accreting then to Gondwana. Further a third model claims Cuyania is para-autochthonous and arrived at its current place by strike-slip faults starting not from Laurentia but from Gondwana. Aftermath As the Taconic Orogeny subsided in Early Silurian time, uplifts and folds in the Hudson Valley region were beveled by erosion. Upon this surface sediments began to accumulate, derived from remaining uplifts in the New England region. The evidence for this is the Silurian Shawangunk Conglomerate, a massive, ridge-forming quartz sandstone and conglomerate formation, which rests unconformably on a surface of older gently- to steeply-dipping pre-Silurian age strata throughout the region. This ridge of Shawangunk Conglomerate extends southward from the Hudson Valley along the eastern front of the Catskills. It forms the impressive caprock ridge of the Shawangunk Mountains west of New Paltz. To the south and west it becomes the prominent ridge-forming unit that crops out along the crest of Kittatinny Mountain in New Jersey. Through Silurian time, the deposition of coarse alluvial sediments gave way to shallow marine fine-grained muds, and eventually to clear-water carbonate sediment accumulation with reefs formed from the accumulation of calcareous