The islands of Trinidad and Tobago lie offshore the coast of northeastern Venezuela, at the southern end of the Lesser Antilles chain. Unlike the latter, which formed by subduction volcanism along the leading (eastern) edge of the Caribbean Plate, Trinidad and Tobago are remnants of compression, deposition, uplift and expansion along the margin of the Caribbean and South American Plates.
As the Atlantic Ocean opened, a process that began 150 million years ago (during the Jurassic Period) and continues today, the North and South American Plates were forced westward and the Caribbean Plate was wedged between them; at the eastern edge of the Caribbean Plate, the American Plates are forced to subduct, producing the volcanic islands of the Lesser Antilles. Meanwhile, along the southern and northern margins of the Caribbean Plate, it has been scraping past the respective American Plates, triggering complex geology resulting from subduction volcanism, tectonic compression and uplift, rifting, deposition and subsequent erosion.
In essence, Trinidad and Tobago lie within a ridge and valley topography (trending southwest to northeast), flooded by the sea; Trinidad lies on the South American Plate while Tobago lies on the Caribbean Plate. Since northwest Trinidad was once connected to northeast Venezuela, it harbors South American fauna and flora (unlike Tobago and the Lesser Antilles). Geologic formations range from Cretaceous to Pliocene across Trinidad and Tobago, representing the span of natural history during which the islands formed; while the geologic strata of Trinidad is complex, Tobago is essentially a ridge of Cretaceous schist, rising above the sea.