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This map was digitized from the geology map of Madagascar (BESAIRIE, 1964).
The 96 original categories were reclassified into predominant rock types
which seem to have an important effect on the vegetation they support.
The categories of sedimentary rocks include sandstones, loose (unconsolidated)
sands, and two limestone categories of different ages (one of which produces
the spectacular "tsingy" areas of jagged, highly eroded limestone pinnacles).
A broad category of metamorphic rocks (including granites and migmatites),
often covered by thick layers of laterites, covers large areas of the central
and eastern areas of the island. Lavas and basalts, and several restricted
rock types including quartzites, marbles and ultrabasics are also distinguished.