Lithgow Mercury October 24th 1924
BLUE MOUNTAINS MAY DISAPPEAR
HOW JENOLAN CAVES BECAME:.
In the course of a lecture at the museum Mr. T. U. Smith, mineralogist declared that some day the great Blue Mountains will be no more. He declared:" All the mountains in the world are gradually being reduced to level plains such as the great western plains of NS Wales, This work of destruction illustrates nature's great art of sculpture Of course, if this work were to continue without interruption all the continents would have been long since reduced to dull monotonous plains, and man would never have reached the civilisation that exists today But nature provides against that. No sooner has she reduced the mountains than she starts to build others by earth movements.
So it is that the landscape that
we see to-day is ever changing and the wonderful scenery of the Blue Mountains,
for instance will some; day pass away and be no more. However, these changes
are so. very
slow and the life of man so short, that he is quite incapable of detecting them, except in a very few
In dealing with the of valleys of the Blue Mountains the lecturer showed that the little insignificant streams, flowing through the valleys' though not wholly responsible for their excavation have actually carried the whole of the material that once filled these valleys. The Blue Mountains are composed of a thick strata of hard sands stone forming the sandstone cliffs of the valleys and underlain by soft shales. When the river commenced its work of cutting through the sandstone, it carved a deep gorge until it reached the soft shales below. when it started to undermine the harder rock until the overburden was too great and the sandstone crashed down and eventually denuded and - carried away by the rivers. Thus the work of widening the valleys commenced and then atmospheric agencies helped in the work as well as numerous streams which flow in from the sides of the valleys.
The lecturer added:- "Not only do rivers act mechanically by cutting away rocks, but they also exert a chemical action by actually dissolving rocks. It is this action which is responsible for the world-famous Jenolan Caves. The rock out of which they have been carved, or perhaps more correctly dissolved, is limestone. All natural water contains gases dissolved from the air, and the most important of these is carbonic acid gas, which is the gas we all exhale. Water charged with this gas is capable of dissolving limestone in the same way in which ordinary water will dissolve sugar. All rocks contain fractures or joint planes which extend from the surface to a great depth below. When a river passes over limestone as it does at Jenolan Caves, some of the water percolates along the joint planes of the limestone and in so doing so dissolves the rock on either side. Thus the fracture becomes wider and wider until at last the river instead of flowing over the surface, goes underground along these widened fractures which form the caves.
"The stalactites and shawls to which the caves owe much of their fame are the visible evidence of the solvent action of the water. As it percolates down from the surface it dissolves out some limestone and eventually forms a little drop on the roof of a cave. This drop is slowly evaporated, and so deposits some of the limestone with which it is charged in the form of calcite. If the drop falls on the floor of a cave before it is evaporated away it will deposit calcite in the same way and so a stalagmite will eventually be formed."