Three Expeditions into the Interior of Eastern Australia Volume II Part 46

Trap-rocks.

Sandstone.

Geological structure and physical outline.

Valleys of excavation.

Extent of that of the c.o.x.

Quant.i.ty of rock removed.

Valley of the Grose.

Wellington Valley.

Limestone caverns.

Description and view of the largest.

Of that containing osseous breccia.

First discovery of bones.

Small cavity and stalagmitic crust.

Teeth found in the floor.

A third cavern.

Breccia on the surface.

Similar caverns in other parts of the country.

At Buree.

At Molong.

Shattered state of the bones.

Important discoveries by Professor Owen.

Gigantic fossil kangaroos.

Macropus atlas.

Macropus t.i.tan.

Macropus indeterminate.

Genus Hypsiprymnus, new species, indeterminate.

Genus Phalangista.

Genus Phascolomys.

Ph. mitch.e.l.lii, a new species.

New Genus Diprotodon.

Dasyurus laniarius, a new species.

General results of Professor Owen's researches.

Age of the breccia considered.

State of the caverns.

Traces of inundation.

Stalagmitic crust.

State of the bones.

Putrefaction had only commenced when first deposited.

Accompanying marks of disruption.

Earthy deposits.

These phenomena compared with other evidence of inundation.

Salt lakes in the interior.

Changes on the seacoast.

Proofs that the coast was once higher above the sea than it is at present.

Proofs that it was once lower.

And of violent action of the sea.

At Wollongong.

Cape Solander.

Port Jackson.

Broken Bay.

Newcastle.

Tuggerah Beach.

Ba.s.s Strait.

GEOLOGICAL SPECIMENS COLLECTED.

As any geological information respecting a country so little known as the eastern coast of Australia may be acceptable to the public, I venture to subjoin a few observations on some of the more prominent subjects of my researches, and I do so with the more confidence because it will appear how largely I am indebted for the interest they possess to the kindness of my scientific friends in England.

CONNECTION BETWEEN SOIL AND ROCKS.

During the surveys and expeditions I carefully collected specimens at every important locality, and I have thus been enabled since my return to England to mark upon my maps the geological structure of the country. By this means also I have been able to determine the relative value of the land in the districts recently explored and to compare it with that of the country previously known.

By a little attention to the geological structure of Australia we learn how much the superficial qualities of soil and productions depend upon it, and where to look for arable spots amid the general barrenness. The most intelligent surveyors of my department have on several occasions contributed considerably to my collection.

Curiosity led me to investigate some of the fossil remains of those lately discovered regions while my public duties obliged me to study also the external features of the country; and I have thus been enabled to draw some inferences respecting various changes which have taken place in the surface and in the relative level of sea and land.

The following are the princ.i.p.al rocks which I noticed in the country.

LIMESTONE.

Limestone occurs of different ages and quality presenting a considerable variety.

1. A light-coloured compact calcareous rock resembling mountain limestone; at Buree and Wellington, rising, at the former place, to the height of about 1500 feet above the sea.

2. A dark grey limestone appears at perhaps a still greater height on the Shoalhaven river; in immediate contact with granite.

3. A crystalline variegated marble is found in blocks a few miles westward of the above, near the Wollondilly.

4. Another variety of this rock is very abundant in the neighbourhood of Limestone plains on the interior side of the Coast ranges and near the princ.i.p.al sources of the Murrumbidgee. This contains corals belonging to the genus favosites; crinoideae are also found abundantly in the plains and distinguish this limestone from the others above-mentioned.

These rocks present little or no appearance of stratification.

A remarkably projecting ridge on the banks of Peel's river contained limestone of so peculiar an aspect as to resemble porphyry, and it was a.s.sociated with a rock having a base of chocolate-coloured granular felspar. (See Volume 1.)

A yellow highly calcareous sandstone, apparently stratified, occurs near the banks of the Gwydir. Large rounded boulders of argillaceous limestone have been denuded in the bed of Glendon brook; and an impure limestone is found in the neighbourhood of William's river, both belonging to the basin of the Hunter and not much elevated above the sea. Calcareous tuff or grit may be observed in various localities, and calcareous concretions abound in the blue clay of almost all the extensive plains on both sides of the mountains.

A soft sh.e.l.ly limestone, most probably of recent origin though slightly resembling some of the oolites of England, occurs extensively on the southern coast between Cape Northumberland and Portland bay where it forms the only rock with the exception of amygdaloidal trap.

GRANITE.

Granite or granitic compounds are more or less apparent at or near the sources of the princ.i.p.al rivers; but with the exception of the Southern Alps and some patches in the counties of Bathurst and Murray this fundamental rock is visible in Australia only where it appears to have cracked a thick overlying stratum of ferruginous sandstone. Thus near the head of the river c.o.x where the latter attains its greatest elevation, and from the character of the valley has evidently been violently disturbed, we find granite in the valley near the bed of the stream.

Observation 1. Such is the character of the country where the waters separate, or in the line of greatest elevation which we are accustomed to term the Coast Range. The general direction of this range is north-north-east and accords perfectly with the hypothesis of Dr. Fitton, founded on the general parallelism observed in the range of the strata, even on the north-western coast, as noticed in his interesting little volume, the first ever devoted to Australian Geology.* The parallelism so remarkable in the range of strata in that portion, the general tendency of the coastlines to a course from the west of south to the east of north on the mainland, and even in the islands west of the Gulf of Carpentaria, and a general elevation of the strata towards the south-east, as deduced from Flinders' remarks, are all facts which should be studied in connection with the direction of the granite along this part of the eastern coast.

(*Footnote. An account of some Geological specimens from the coasts of Australia by William Henry Fitton, M.D., F.R.S., V.P.G.S., etc. 1826.)

Observation 2. It may be also observed that the sandstone reposing on the rock eastward of this division or watershed is slightly inclined towards the sea, whereas all the sandstone on the interior side, or westward of it, dips to the north-west.

TRAP-ROCKS.