The Bouguer anomaly map of Viti Levu in the Fiji Group consists essentially of a gravity “low” surrounded by gravity “highs”. The “low” can be explained partly by the effect of the younger rocks which have a specific gravity 0.4 g/cm3less than the older rocks (Lower Tertiary), and partly by a relative thickening of the crust by about 10 km. The average crustal thickness is about 30 km which supports the geological evidence that the Fiji islands are continental.