Three Expeditions into the Interior of Eastern Australia, Volume 2 / With Descriptions of the Recently Explored Region of Australia Felix, and of the Present Colony of New South Wales

by T. L. Mitchell

AGE OF THE BRECCIA CONSIDERED.

Nothing could be discovered in the present state of these caverns at all likely to throw any light on the history or age of the breccia, but the phenomena they present seem to indicate more than one change in the physical outline of the adjacent regions, and probably of more distant portions of Australia; at a period antecedent to the existing state of the country.

STATE OF THE CAVERNS.

Dry earth occurred in the floor of both the caverns at Wellington Valley and in the small chamber (Plate 28) of the breccia cave it was found, as before stated, beneath the three lines of stalagmite and the osseous breccia. It seems probable therefore that this earth once filled the cave also to the same line, and that the stalagmite then extended over the floor of red earth. Moreover I am of opinion that the interval between the stalagmite and the roof was partly occupied by the bone breccia of which portions remain attached to the roof and sides above the line of stalagmite. It is difficult to conceive how the mass of red earth and stalagmitic floors could be displaced, except by a subsidence in the original floor of the cave. But the present floor contains no vestiges of breccia fallen from the roof, nor any remains of the stalagmitic crust once adhering to the sides, which are both therefore probably deposited below the present floor.

PLATE 50: MARKS OF SUBSIDENCE IN AN INNER PORTION OF THE BRECCIA CAVERN.
Major T.L. Mitchell del. Scherf Lith. J. Graf Printer to Her Majesty.
Published by T. and W. Boone, London.

In the external or upper part of the same cave, as shown in Plate 45, the floor consisted of the red dust, and was covered with loose fragments of rock, apparently fallen from conglomerated masses of limestone and breccia which also however extended under the red earth there. Thus it would appear that traces remain in these caverns: First, of an aqueous deposit in the red earth found below the stalagmite in one cavern, and beneath breccia in the other. Secondly, of a long dry period, as appears in the thick crust of stalagmite covering the lowest deposit in the largest cavern, and during which some cavities were filled with breccia, even with the external surface. Thirdly, of a subsidence in the breccia and associated rocks and, lastly, of a deposit of red earth similar to the first.

TRACES OF INUNDATION.

The present floor in both caves bears all the evidence of a deposition from water which probably filled the interior of the cavern to an unknown height. It is clear that sediment deposited in this manner would, when the waters were drawn off, be left in the state of fine mud, and would become, on drying, a more or less friable earth.