Typically we think of caves forming in carbonate rocks, such as limestone and marble, and other types of rocks that dissolve. This is because carbonate rocks are highly susceptible to the action of carbonic acid in rainwater and groundwater. Lowering the land surface by carbonation is a comparatively rapid process in areas underlain by limestone and marble, and where rainfall is abundant. Sulfuric acid is also known to form caves, particularly noteworthy in arid regions. Similar sulfuric acid reactions also operate in humid regions but tend to be masked by carbonation (Berger 1995). Other processes are at work forming caves in areas not underlain by carbonate or evaporite rocks.