<em>there are 9 on the main land and 13 in total</em>
The limestone caves at Carlsbad Cavern were formed by hydrogen-sulfide-rich (H2S) waters. This water moved through fractures and faults in the limestone and mixed with rainwater along the way. The mixture gave rise to a substance known as sulfuric acid (H2SO4). Sulfuric acid is able to dissolve limestone, eventually creating Carlsbad Cavern. The process of cave formation ended roughly four million years ago.
The sea is the interconnected system of all the Earth's oceanic waters, including the Atlantic, Pacific, Indian, Southern and Arctic Oceans. However, the word "sea" can also be used for many specific, much smaller bodies of seawater, such as the North Sea or the Red Sea.
