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disturbances which dislocated another member of the series, namely the arenaceous fossiliferous rock, -which rests upon the slaty limestone. Effects of this event may be seen, in New South Wales, at St. Patrick's Plains and on Harper's Hill.
The latest eruption seems to have been that which intervened between the above-mentioned epoch and the following one, characterised by the deposition of coal. Its traces are visible on Mount Tomah in New South Wales, and on Mount Wellington and Dry's Bluff in Van Diemen's Land. They show that all the members composing the series belonging to the second epoch were affected by similar disturbances. In the case of the two latter localities, the eruption was of very limited extent; so that, while on the N. W. of Mount Wellington a part of the series is not disturbed, on the S. E. three of its newest members are dislocated, and the uppermost is severed, and elevated 2500 feet above the others. At Dry's Bluff, where the whole series is disturbed, the dislocated part is separated from the rest, to a superior height of 3900 feet. (PL V. fig. 2.)
An inspection of the annexed map, in which the crystalline and sedimentary rocks of the preceding epoch are represented by the yellow colouring, will show, at the first glance, that the manner in which the mineral masses of that epoch were added to the original ground-work gave rise to the formation of basin-shaped localities, singularly adapted to the developement of the phenomena into which we are now about to inquire.
Three of these local ties deserve particular attention. The first, in New South Wales, presents but the westerly marginal portion of a once great basin, which portion is now watered by the tributaries of the rivers Hunter and Hawkesbury, and which we shall call, for convenience sake, the Newcastle Basin.
The second, the South Esk Basin, in Van Diemen's Land, is confined partly to the vales of Avoca and Break-o'-day, partly to the country watered by the Macquarie and Blackman's rivers.
The last, the Jerusalem Basin, also in Van Diemen's Land, includes the Derwent valley as far north as Hamilton and Bothwell, together with the Richmond and Coal River valleys, and presents, like the basin of New South Wales, no more than its westerly and northerly sides unaltered; its extent to the south and east being only indicated by the geological features observable on Maria Island and Tasman's Peninsula.
The walls of the three basins appear to have a contemporaneous origin; but the deposits which they include seem to differ in point of date, and lead to the belief that the geological conditions under which they were produced were modified, in each locality, not only with respect to time, but as regards the nature of coal and other strata which they contain.
We shall now briefly pass in review the geological evidence observable in each of these localities.
The point from which the most comprehensive view of this basin may be obtained is Port Stephen.
There lies between that locality and the river Hunter, a small ridge, dividing the drainage of the river William from that of the Karua. This ridge is composed of breccia, gritstone, greenstone, and basalt. On its southern flank lies a coarse sandstone, containing conularice, spiriferce, and produdce, subjacent to a conglomerate: these rocks constitute the uppermost members of the series of strata described in the preceding epoch, and both extending to the left bank of the Hunter. About the site of Raymond Ferry, the two members are found, at the level of the river, dipping to the south.
On crossing the Hunter, and taking a southerly course, we come on a ridge ranging E. and W., and composed of masses of sandstone, differing from that of the left bank of the Hunter. It is fine grained, contains mica and iron glance, and is in some places variegated by zones of different colours, in others interspersed with very thin seams of coal. On the southern side of the ridge, at Lake Macquarie, coal crops out from beneath this sandstone.
Should we now take an easterly course from the above locality until we reach the sea shore, and then proceed northerly, we should come in sight of a cliff, 200 feet high, and about 2000 feet long, displaying several seams of coal, arranged in parallel beds, of which the continuity is interrupted by faults, beautifully illustrating the dislocation of coal strata. (Pl.V.fig.1.)
At the Island of Nobby, which stands between the cliff above mentioned and the opposite point of land forming the north head of Port Hunter, we find the coal strata dipping southward, and at the same angle of inclination at which we found the sandstone with spiriferce and conularice dipping at Raymond Ferry.
On St. Patrick's Plains and the river Wolombi analogous relations between siliceous breccia, conglomerate, fossiliferous slaty rock, coal, and fine-grained sandstone are observable, confirming the inference that the ridge of siliceous breccia, greenstone, and basalt, between Port Stephen and the river Hunter, is part of the north-eastern margin of Newcastle Basin; and that the coarse sandstone with spiriferce and conularice, with incumbent conglomerate (Raymond Terrace), is the floor of its coal deposits.
The seams of coal in the cliff above referred to, are not there accessible, but they may be examined in any of the coal-pits which are sunk on the sloping side of the elevation. That which is nearest to the fall of the cliff, gives the following section, in the ascending order: —
A. Coal (the lowest of the deposit) - - - 3
B. Greenish sandstone - - - - 50
C. Coal - - - - - -3
D. Greenish sandstone with blue veins - - 2.5
E. Coal ..---. 5
F. Clay rock (greyish), and shale (bluish), with impres
sions of Sphenopteris lobifolia, Sphenopteris alata,
G. Coal - - - - - - 5
H. Cherts, gritstones, with angular fragments of flint
intermixed with thin veins of coal - - 44
I. Coal - - - - - - 3
K. Conglomerate (the uppermost of the deposit) . 23
Besides the impressions of Phyllotheca and Glossopteris, there was also discovered an impression of a fish, but too imperfect to allow of the determination of its character.
To the westward and southward of the cliff above described, the conglomerate K. of the coal deposit is seen dipping to the westward, under masses of variegated and fine-grained micaceous sandstone, which, in that direction is found gradually to rise to the height of 3000 feet; attaining, in some places, a thickness of 1400 feet, as may be observed in the valley of the Grose.
The average strike of this sandstone on the northeastern margin of the basin is S. E.; on the westerly margin it is E.; at the southern side, which is about Hlawara, its strike is N. W.; the strata thus seeming to converge towards the county of Cumberland, the probable centre of the basin.
The variegated sandstone about Newcastle lies in a position conformable to the coal deposits; as is again the case with the latter, in relation to the Raymond Terrace conglomerates and sandstones, containing spiriferce, productce, and conularice.
SOUTH ESK BASIN (VAN DIEMEN'S LAND).
This basin is very limited in extent, and displays a margin much indented. Its section, taken from east to west, that is from St. Patrick's Head to Ben Lomond, presents, first, a greenstone axis, against which are abutted greywacke, clay slates, and grits, in vertical positions; next, a limestone rock, with spiriferae, and a conglomerate, in horizontal beds; then, on the southern side of Ben Lomond, a seam of coal, over which lies a conglomerate and a variegated sandstone. The three last members of the deposits are dislocated, and uplifted 2100 feet above the actual level of the coal-beds. In this basin the variegated sandstone occupies the uppermost position amongst the sedimentary rocks.
In going from the Eastern Marshes to Jerusalem, we observe, first, a limestone rock, containing productce and spiriferce; then, a conglomerate; and then, an outcrop of coal seams, — all dipping south. In Jerusalem coal-pits, the artificial section presents the following sequence of coal-beds, taken in the ascending order:—