North Island [North Island, Seychelles]

North Island has an area of 201 ha, and is the ninth largest of the granitic Seychelles Islands. At its highest point (Grand Paloss) it reaches over 180 m above sea level. The island's north-south axis is made up of raised rocky hills with an outlier (Congoment) to the east. Along the eastern and western sides of the island are two large low-lying "plateau" areas. Geologically, the island differs from most of the granitic islands of Seychelles apart from its nearest neighbour Silhouette. Both islands are made up of syenite resulting from volcanic activity. These rocks are of much more recent origin than the bulk of Seychelles granite; Mahe and Praslin granites have been dated at about 650 million years old and Silhouette syenite at 63 million years old. The plateaux are made up of recent calcareous sediments covered (on the landward side) with 20-30 cm depth of weathering products from the syenite hills and, in places, marsh deposits.