a) The Interior Mountain Ranges have a maximum elevation of 2,254 m and dominate the eastern half of the island; define a WNW-ESE orographic bend which forms the core of the island and controls the rainfall on the island. The rocks here are comprised of island arc derived Cretaceous and early Tertiary volcaniclastic sediments, andesitic, granodiorite and subordinate basic volcanic rocks, limestone and metamorphic rocks. The bedrock is fractured and deeply weathered to a depth of about 10 m, sometime more, and is overlain by approximately 1.0 m thick layer of lithosols. Structurally, these mountains are dominated by faulting. The river valleys are fault-controlled and deeply incised where steep slopes are predisposed to slope failures.

b) The Tertiary Limestone Plateau occurs as a highly dissected upland region between 700-1000m in elevation in the central and western part of the island. It is largely made up of karstic limestone with subordinate clastic rocks that fringe the interior mountain ranges and covers upto 65% of the total surface area of the island. The bedrock is highly faulted and major fault scarps are presented. The lithosols are shallow and bauxite deposits overlie the bedrock in the central part of the island.

c) The Alluvial Fans and Interior Valley Deposits (poljes) comprise quaternary sediments. Alluvial fans are best developed along the south coast where they form narrow plains fringing the upland landforms. They may be regarded as faulted mountain fronts. Some of the fans appear to be dominated by debris flow deposits. Plains of Liguanea and St. Catherine are the best examples. Most of the urban centres and agricultural and industrial activities on the island are located on quaternary sediments.