Denis

Denis is one of the northernmost islands of the Seychelles lying around 80 kilometres North of Mahe, the largest of the granitic Seychelles, at the northern edge of the Seychelles Bank. It is approximately 140 ha in area (Directorate of Overseas Survey (UK)/Seychelles Government, unpublished data), although there is evidence of rapid erosion in the past. The maximum elevation is less than 4 m above sea level and average surface elevation is probably around 2.5 m. Unlike the majority of islands on the Seychelles Bank, Denis has no granite and it is formed entirely of reef-derived sands. The deposition of guano on sand deposits has led to the formation of phosphatic sandstone over 80% of the island's surface. Much of the guano that originally overlaid this cemented layer has now been removed for export. Guano removal left parts of the island bare of soil. In phosphatic sandstone areas where soil cover has survived, soils of the Jemo Series occur; the rest of the island has Shioya series soils. In some wetland areas, brown loams rich in phosphate (leached from phosphatic rocks) occur. Denis has a number of marsh areas, although the extent of marshland appears to have been greater in the recent past. At the time of the surveys, wetlands were limited in extent and most showed some marine influence.