Why are Basse-Terre and Grande-Terre called twin islands?

Basse-Terre and Grande-Terre are referred to as twin islands because they constitute the core of the French overseas département of Guadeloupe and are situated immediately adjacent to one another, separated only by a narrow channel known as the Salée River.123

Despite their proximity and shared status as the heart of the territory, the two islands are geologically distinct. Basse-Terre is part of the inner, mountainous, and volcanic arc of the Lesser Antilles, characterized by lush vegetation and significant elevation, including the active Soufrière volcano. In contrast, Grande-Terre belongs to the outer limestone arc; it is a low-lying, drier island with sandy soils and scrub forest, serving as the economic hub of the region.134