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A. Coal (the lowermost) - - - -2
B. Blackish clay, with impressions of Pecopteris au-
C. Greyish clay - - - - - 11
D. Blackish clay, with the impressions of the clay B. - 3
E. Greyish clay - - - _ - 12
F. Coal - - - - - -3
G. Blackish clay, with impressions similar to the clay
B. and D. - - - - 2
H. Grey clay - - - - - 2
I Clay slate - - - • 1
K. Greenish sandstone - - - - 3
L. Sandstone, with impressions of Pecopteris odon
topteroides - - - - - 13
In the southern dip, which it assumes, the sandstone L. may be followed up to Richmond, where it is found, as at Jerusalem, on the top of the coal.
Beyond Richmond it may be further traced to the edge of the sea at Pitt's Water; and at the coal-pits of Port Arthur it is again found cropping out with coal. The coal deposit of those pits, taking all the beds together, has a total thickness of 150 feet; its two uppermost seams correspond with the two coal seams, A and F, noticed in the pits of Jerusalem, as do also the intervening shales in respect to their fossil plant impressions.
At the settlement of Port Arthur, farther south than the coal-pits of the same name, the sandstone only is to be seen, dipping, as it were, under masses of clays which compose the island of Point Puer, and which contain Pachydomus globosus.
The line which we have just reviewed, that is, that from Eastern Marshes, over Jerusalem, Richmond, to Point Puer, is dislocated in many places by greenstone; and the evidence it furnishes would therefore be of little value, had not the Jerusalem Basin presented additional evidence regarding the order of superposition.
These localities are,—the estate of Mr. Parsons, not far from Bothwell; Jericho; Nine Mile Marsh; London Inn, Spring Hill; Research Bay; South Port; and Maria Island. At the locality of London Inn, a section taken in a well sunk close to a police station, when I was engaged in exploring that part of the island, identify the sandstone of that locality with that of the Jerusalem coal-pit, as beneath it was the shale with the impression of Pecopteris australis and Zeugophyllites overlaying a seam of coal.
If we draw a line from London Inn to Hobart Town, it would correspond in direction with that drawn from the Eastern Marshes, through Jerusalem, Richmond, and Port Arthur, to Point Puer, and would cut through the following successions of rocks: a sandstone with impressions of Pecopteris odontopteroides superposed by masses of clay, lying on the side of Spring Hill, and containing Pachydomus globosus.
Both the sandstone and clay dip S. W. About Greenpond and Brighton these masses are succeeded by a different sandstone, which is fine, micaceous, and without impressions of Pecopteris. At Hobart Town it is overlayed by a yellow limestone rock, containing Bulinus and Helix.
The first line showed, then,—
2. Shale, with impressions of Pecopteris australis and Zeugophyllites.
3. Sandstone, with impressions of Pecopteris odontopleroides.
4. Masse of clays, with Pachydomus globosus
The second, conjointly with the section of the well at London Inn, —
2. Shale, with impressions of Pecopteris australis and Zeugophyllites.
3. Sandstone, with impressions of Pecopteris odontopteroidts.
4. Masses of clays, with Pachydomus globoawt.
5. Variegated sandstone.
6. Yellow limestone, with Bulinus and Helix.
The two above lines are greatly dislocated by greenstones and basalts, and do not offer a continuity of the enumerated members: both need are-examination, by which the fact of the clays with Pachydomus existing in the position which apparently they occupy would be confirmed; and thus the question regarding the relative age of this coal solved. Until then, we can only admit as possible that the Jerusalem coal deposit may be somewhat anterior in date to those of the South Esk and Newcastle basins.
With the deposits of the three above-described basins we may connect partial outcrops of coal observed in a small valley called the Reedy Valley (the Vale of Clywd), north of Mount York, and east of Mount Clarence, and which seemingly belong to the Newcastle basin; a probability, however, rather invalidated by the fact of the coals overlaying masses of pure bitumen, — a circumstance not discovered to exist elsewhere.
The outcrops of coal observed by the late surveyor-general Oxley, to the northward of Port Stephen, at the heads of the rivers Hastings and MacLeay; those, again, noticed by Cunningham, at Moreton Bay, together with the outcrops of coal at Western Port,—are most probably indications of the margins of basins similar to that of Newcastle.
In all these outcrops of coal, masses of variegated sandstone appear above the coal strata: and this fact, connected with others, obtained in the examination of the Newcastle, South Esk, and Jerusalem basins, and of other tracts of the country, leads to the conclusion that the variegated sandstone about Sydney, with the vaiiegated sandstone and yellow limestone, with Bulimia and Helix, of Hobart Town, and above which no other formation has yet been found, constitute the highest beds in geological series of the two colonies.
MTNERALOGICAL DESCRIPTION OF ROCKS BELONGED TO THE DESCRIBED EPOCH, INCLUDING AN ANALYSIS OF SOME LIGNITES FROM ALLUVIAL DEPOSITS HI VAN DDSMEN'S LAND.
In the subjoined mineralogical description of some varieties of coal belonging to New South Wales and Van Diemen's Land, the specific gravity spoken of, has been ascertained by myself, through the means of a Nicholson's hydrostatic balance, capable of indicating distinctly differences equal to 4(^0oth part of the weight in the balance. The chemical character of each species and variety I have ascertained by two different analyses: —
1st. By that of separating the organic substance under examination into its proximate constituents.
2nd. By that of resolving it into its ultimate elements.
In the first analytical process, one portion of known quantity of coal was deflagrated by a known quantity of nitre ; another portion was distilled in a small glass retort, — and the vapours which distillation yielded were condensed, as also the gases collected over water, into a graduated receiver. Thus, the quantity of charcoal, bitumen, earthy constituents, coke, and coaltar was ascertained; and a further determination was made of the amount of carbonic acid, sulphuretted hydrogen, and the two sorts of carburetted hydrogen, contained in the gas receiver, by treating the gaseous mixture alternately with caustic potassa, carbonate of lead freshly precipitated from the acetate, and finally, with chlorine gas, both in darkness and in light.
In the second process, the elegant apparatus of GayLussac and Liebig was made use of, and the oxide of copper freshly prepared employed as the oxydising agent. The carbon was estimated from the amount of carbonic acid absorbed by the balls containing caustic potassa, and the hydrogen from the amount of water absorbed, as shown by the increase in weight of the tube containing chloride of calcium. The oxygen was estimated from the loss of weight of the combustion tube, deducting the carbon and hydrogen, as also the nitrogen, which was previously ascertained.*
Colour, black, with a slight tinge of grey; structure foliated; fracture even, the fragments of indeterminate form; it soils the fingers, and is soft and brittle; specific gravity, 1-31.
Chemical Character. — It burns easily, with a reddish flame; swells and agglutinates; its constituents are —
Charcoal - - - ^62*8
Bitumen .... 25*2
Earthy matter - - - 12*2
One pound yields 1 foot 1*806 cubic inches of
* I shall seize this opportunity of offering my sincere and public acknowledgments to William Pngh, M.D., of Launceston, Van Diemen's Land, who, during my stay in that island, has lent me the use of his laboratory, and in many instances his personal co-operation, in the analysis of the Australian minerals and soils. Not less sincere thanks are due to Mr. Richard Phillips, F. R. S., and Mr. Richard Phillips, Jun., with whose able assistance I was enabled, last year, to complete, in the Laboratory of the Economic Geology, the remainder of the analyses, the result of which will be detailed in the Agricultural Section of this volume.