pl.xiii.f.

9).
The description here given is deduced from the natural appearances under the lens, and not from artificial or regular sections.

But the specimen admits of a partial substitute for this; for the surface is worn down and roughly polished, as is the case with all the exposed surfaces of ancient limestones in Australia; the result probably of the acidulous properties of rain water, or of the atmosphere, which, in a tropical climate, where violent showers alternate with great drought, is capable of producing various sensible changes in rocks in a long series of ages.

Many rocks of limestone in New South Wales, even harder than the Burdekin marble, are actually grooved in short parallel furrows, over wide surfaces, and along their sides, by some similar agency.].