sandstone caves

   Most natural sandstone caves are surface river-cut notches at the foot of rock cliffs, or left part way up the cliff due to later downcutting. This origin accounts for most of the caves once inhabited by the Pueblo Indians in the sandstone cliffs of the western USA. True caves do occur in sandstone and some of these appear to be at least partially of dissolutional origin. Their existence probably reflects matrix leaching by ground water moving through zones of especially high primary porosity and permeability. Though sandstones with a calcite matrix cement are more prone to such development, even siliceous cement, which has a very low solubility in water, may be removed during a sufficiently long time span. The sandstone caves of the Sarisarinama Plateau, Venezuela may be a special case of this type of development. These include shafts 300m in diameter and 200m deep, and passages up to 500m long. They were probably cut in the quartz sandstone by underground streams, after early leaching of the cement by hydrothermal solutions, and the shafts have been modified by later collapse [9].