Final answer:
Most caves of significant size are formed in limestone by the dissolving activity of groundwater. When groundwater containing atmospheric CO2 finds its way into microscopic cracks in the limestone deposits, CaCO3 dissolves in the acidic solution and gradually enlarges the cracks until a cave is formed.
Step-by-step explanation:
Most caves of significant size are formed in limestone by the dissolving activity of groundwater. When groundwater containing atmospheric CO2 finds its way into microscopic cracks in the limestone deposits, CaCO3 dissolves in the acidic solution. Over time, the cracks enlarge and a cave is formed. Water from the surface seeps into the cave and forms stalactites and stalagmites.