... 2009, the New 7 Wonders Foundation, which runs the New Seven Wonders of the World program, included Halong Bay on its list of nominations as one the World's 7 Natural Wonders.[edit] Geology ... Silurian periodIt underwent a phase of inverse-motion that created mountains deep under the water.420,000,000-340,000,000 BCend of the Silurian period and throughout the whole Devonian periodThe ... carbon dioxide, which has a deleterious effect on the caves. The mouths of some caves have been widened to allow for tourist access. This increase in light has led to an imbalance in the delicate...