The following facts are summarised from the geology of Queensland written by Mr. Daintree, as the result of his investigations, whilst prosecuting the search for new goldfields on behalf of the Queensland Government in the northern portion of their territory, as also from the official reports of the Geologist of Southern Queensland, and other sources.

The consideration and history of the different formations will be taken in their sequence of time, as far as the stratified or sedimentary rocks are concerned. The igneous rocks will be described under the various groups of Granitic, Trappean, and Volcanic.

_Aqueous_:-- Alluvial (recent).

Alluvial, containing extinct faunas.

Desert sandstone, Cainozoic.

Cretaceous } Oolitic } Mesozoic Carbonaceous } Carboniferous } Palaeozoic Devonian } Silurian } _Metamorphic._

Alluvial.--Fresh-water deposits skirt all the present watercourses, but the acc.u.mulations are insignificant on the eastern watershed, except near the embouchures of large rivers, such as the Burdekin, Fitzroy, etc. On the sh.o.r.es of the Gulf of Carpentaria, however, and in the south-western portions of the colony, where the watercourses have scarcely any fall, and where in seasons of excessive rain the country is nearly all inundated, fluviatile deposits are very extensive. Though the dense lavas of the Upper Burdekin (volcanic outbursts of a late Tertiary epoch) are traversed by valleys of erosion, in some cases 200 feet deep, and five miles broad, yet very narrow and shallow alluvial deposits skirt the immediate margin of the watercourses draining such valleys. It is only near the mouths of the larger rivers that any extent of alluvium has been deposited, and even these areas are at the present time in seasons of excessive rain, liable to inundation, showing that little upheaval of this portion of Australia has taken place since the last volcanic disturbances terminated.

The meteorological or climatic conditions during this period were nearly identical with those of the present time, heavy rains during the summer months causing violent floods, removing seaward the aerial decompositions and denuded materials from year to year.

What lapse of time is represented during this period of erosion is a matter of speculation, but it seems certain that the mollusca of the present creeks were also the inhabitants of the waters during the whole period of denudation since the last volcanic eruption.

From the Gulf of Carpentaria in the north, to Darling Downs in the south, however, the fossil remains of extinct mammalia have been found in breccias and indurated muds, which are the representatives of the beds of old watercourses through which the present creeks cut their channels. At Maryvale Creek, in lat.i.tude 19 deg. 30 sec. S., good sections of these old brecciated alluvia occur. The fossils from this section, as determined by Professor Owen, are "Diprotodon Australis, Macropus t.i.tan, Thylacoles, Phascolomys, Nototherium," crocodile teeth, etc.

Imbedded in the same matrix occur several genera of mollusca undistinguishable from those inhabiting Maryvale Creek.

The fact of these older alluvia forming both the bed and the banks of the present watercourse, goes to prove that Diprotodon and its allies inhabited the Queensland valleys when they presented little difference in physical aspect or elevation from that of the present time. The crocodile (Crocodilus Australis), however, had then a greater range inland than it has now. A study of these Diprotodon breccias leads to the conclusion that the remains are chiefly entombed in what were the most permanent waterholes in seasons of excessive drought, and that the animals came there in a weak and exhausted state to drink and die, just as bullocks do under similar conditions at the present time.

No human bones, flint flakes, or any kind of native weapons have yet been discovered with the extinct mammalia of Queensland.

CAINOZOIC.

Desert Sandstone.--On the eastern branches of the Upper Flinders and elsewhere, fine sections are exposed of lava resting on horizontal beds of coa.r.s.e grit and conglomerate, which lie in turn unconformably on olive-coloured and gray shales with interstratified bands and nodules of argillaceous limestone containing fossils of cretaceous affinities. I have called this upper conglomerate series "Desert Sandstone," from the sandy barren character of its disintegrated soil, which makes the term particularly applicable.

Without doubt, it is the most recent widely-spread stratified deposit developed in Queensland. The denudation of the "Desert Sandstone" since it became dry land has been excessive, but there still remains a large tract "in situ," and all the available evidence tends to show that this "Desert Sandstone" did at one time cover nearly, if not quite, the whole of Australia. The journals of the two Gregory's description of the new settlement of Port Darwin, all bear evidence to the continuity of this so-called "Desert Sandstone" over all the extended areas investigated by them.

Augustus Gregory's description of the sandstones of the Victoria River agrees with those of the "Desert Sandstone" of Queensland, the specimens from either locality being undistinguishable the one from the other, while the same barren soil, the same hostile spinifex, the same fatal poison plant, mark its presence from Perth to Cape York.

In Queensland, the upper beds are ferruginous, white and mottled sandy clays, the lower being coa.r.s.e alternating grits and conglomerates; the extreme observed thickness has not exceeded 400 feet. A characteristic view of the upper "Desert Sandstone" beds is shown in Betts' Creek, on the Upper Flinders. Whether these are marine, lacustrine, or estuarine deposits, there is hardly sufficient evidence to show.

What may be the value of this "Desert Sandstone" for free gold, is at present unsolved; but the very nature of its deposition seems to preclude the idea that that metal will be found in paying quant.i.ties, except where direct local abrasion of a rich auriferous veinstone has furnished the supply.

MESOZOIC.

Cretaceous.--As early as 1866 a suite of fossils was collected by Messrs. Sutherland and Carson, of Marathon station, Flinders River, and forwarded for determination to Professor McCoy, in Melbourne. They were never figured, but his ma.n.u.script names are as follows:--

_Reptilia._

Ichthyosaurus Australis. "M'Coy."

Plesiosaurus Sutherlandi.

Plesiosaurus macrospondylus. "M'Coy."

_Cephalopoda._

Ammonites Sutherlandi. "M'Coy."

Ammonites Flindersi. "M'Coy."

Belemnitella diptycha. "M'Coy."

Ancyloceras Flindersi.

_Lamellibranchiata._ Inoceramus Carsoni. "M'Coy."

Inoceramus Sutherlandi. "M'Coy"

(identical with the English species I. Cuvieri).

In company with Mr. Sutherland, who supplied McCoy with the before-mentioned materials, Mr. R. Daintree visited the Upper Flinders, and carefully collected the fossils from three localities, viz., Marathon station, Hughenden station, and Hughenden cattle station.

At Marathon, which is some forty miles further down the Flinders than Hughenden, there is, close to the homestead, an outcrop of fine-grained yellow sandstone, which has been quarried for building purposes, and below this, to the edge of the waterhole supplying the house, is a series of sandstones and argillaceous limestones, containing numerous organic remains. These were submitted to Mr. Etheridge for examination and correlation, the result of which appears in the appendix to his work. The Hughenden cattle station is twenty miles further up the Flinders than the Hughenden head station. Here hundreds of Belemnites are strewn over the surface of the two ridges which front the cattle station huts, but they are rarely found in the soft shales which crop out from under an escarpment of "Desert Sandstone." The lithological character of these cretaceous strata is such that decomposition is rapid; the resulting physical aspect being that of vast plains, which form the princ.i.p.al feature of Queensland scenery west of the Main Dividing Range; but that the "Desert Sandstone" has extended over all this country is evidenced by its existence either in the form of outliers, or as a marked feature "in situ" in all main watersheds, or by its pebbles of quartz and conglomerate, which are strewn everywhere over the surface of the plains. The height of the watershed between the Thomson and Flinders Rivers is locally not more than 1,400 feet above sea level, and as the former river has to travel as many miles before reaching the sea, it is easy to understand why, in a country subject to heavy tropical rains at one period of the year, followed by a long dry season, the river channels are ill-defined, and vast tracts of country covered by alluvial deposits. Down the Thomson and its tributaries, these mesozoic rocks are known to extend, though much obscured by flood drifts. That this portion of the mesozoic system extends throughout the whole of Western Queensland to Western Australia is also more than probable, hidden, however, over large areas by "Desert Sandstone."

Mineral Springs.--There is one other subject of practical interest connected with the great mesozoic western plains, and that is the occurrence of hot alkaline springs, which suggest the possibility of obtaining supplies of water on the artesian principle over some portion at least of this area.

At Gibson's cattle station, Taldora, on the Saxby River, a tributary of the Flinders, a spring of hot water rises above the surface of the plain, and its overflow deposits a white encrustation, which on a.n.a.lysis by Dr. Flight, under the direction of Professor Maskelyne, afforded:--

Water 27.793 Silica 0.600 Chlorine 3.369 Sodium 2.183 Carbonic Acid 33.735 Soda 31.690 ------ 99.370

Apart, therefore, from the 5.552 per cent. of chloride of sodium, the deposit consists of sequi carbonate of soda or native "Trona," and as such is used by the settlers for culinary purposes, etc.

PALaeOZOIC.

"Carboniferous."--Whilst the affinities of the southern coalfield of Queensland are mesozoic, a northern field, of even larger extent, has a distinct fauna more resembling the Palaeozoic Carboniferous areas of Europe.

The Dawson, Comet, Mackenzie, Isaacs, and Bowen Rivers drain this carboniferous area; and numerous outcrops of coal have been observed on these streams. No commercial use, however, has yet been made of any of these deposits, as the measures generally are too far inland to be made available until the railway system of the country is extended in that direction.

"Devonian."--From the southern boundary of Queensland up to lat.i.tude 18 deg. S., a series of slates, sandstones, coral limestones, and conglomerates extend to a distance 200 miles inland; these are sometimes overlain by coal measures, sometimes by volcanic rocks, and consequently do not crop out on the surface over such districts. North of lat.i.tude 18 deg. S., however, over the Cape York Peninsula, this series (so far as we have any evidence), is absent, granites and porphyries capped by "Desert Sandstone" forming the ranges on the eastern, and their abraded ingredients the sandy ti-tree flats, those on the western side of that inhospitable tract of country, a never-ending flat of poor desert-looking sandy ti-tree country, stretching away to the sh.o.r.es of the Gulf of Carpentaria.

In the limestone bands, which form the lower portion of the series, corals are very numerous; in fact, the limestones, where little alteration has taken place, are a ma.s.s of aggregated corals; and as this cla.s.s of rock has resisted aerial destruction better than the a.s.sociated slates and sandstones, the barriers thus formed mark the trend of the rock system to which they belong, in a very picturesque and decided manner; their bold, ma.s.sive, and varied outline chiselled into the most delicate fretwork by Nature's hand, is relieved by a wealth of richly-tinted foliage, unknown in the surrounding bush; and the eye jaded with the monotony of the eternal gum tree turns with delight to the changing tints and varied scenery presented by these barrier-like records of the past. This cla.s.s of country is very much in evidence at Chillagoe. On the track from the Broken River to the Gilbert diggings, Devonian rocks several thousand feet thick may be observed, as they are continuous in dip, without being repeated, for at least five miles across the strike, with an average inclination of 60 deg.

Although on the Broken River and its tributaries a breadth of thirty miles with a length of sixty miles, is occupied by a persistent outcrop of Devonian strata, gold has only been discovered in remunerative quant.i.ties in a small gully, where a trapd.y.k.e has penetrated the Palaeozoic rocks of the district.

The following districts, however, where Devonian rocks prevail, have been the centres of gold mining enterprise:--Lucky Valley, Talgai, Gympie, Calliope, Boyne, Morinish, Rosewood, Mount Wyatt, Broken River, portion of Gilbert.

In every case here cited, the country is traversed by trap rocks of a peculiar character, either diorite, diabase, or porphyrite; and tufaceous representatives of these are also found interstratified in the upper portion of the same formation, and occasionally throughout the other beds.

At Gympie, the auriferous area is confined to veins traversing a crystalline diorite, or within a certain limit of its boundary, marked by the presence of fossiliferous diabase tufas.

Whatever may have been the solvent and precipitant of the n.o.bler metals in the auriferous veinstones a.s.sociated with trap intrusions, all other but hydrothermal action may safely be eliminated, the very nature of the reefs, composed as they are of alternating layers of a promiscuous mixture of quartz, calcspar, pyrites, etc., affording unmistakable evidence on this point. The gold also contained in the trap d.y.k.es themselves is always accompanied by pyrites, both (according to Daintree), hydrothermal products separating out during the cooling down of the trap intrusions. Auriferous lodes, occurring in areas where hydrothermal action has attended trap disturbances of a special character in Queensland, are generally thin--to be estimated by inches rather than feet; but taken as a whole they are far richer in gold than those enclosed by sedimentary rocks.

GRANITIC.

Outcrops of granite extend along the eastern coast of Queensland from Broad Sound to Cape York, and inland as far as the heads of streams running direct from the inner coast range to the sea.

Very little rock of this character is met with west and south of the Dividing Range which separates rivers flowing to the eastern and northern coast, and those trending south to the Murray or Cooper's Creek.