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organic remains, which will be fully described in the Zoological Section of this work.
Arguxaceous Or Clay Slates.
The clay slates which appear in the second epoch greatly differ, in a mineralogical point of view, from from those described under the first. They seldom possess a foliated structure; on the contrary, their stratification is often indistinct, and the fracture either slaty, conchoidal, or splintery. The numberless varieties of the rock, many of which differ only in colour, may be arranged under three species.
Var. 1. Common Clay Slate (shiste argileux).
Its colours are various: sea-green, yellow, bluish black, pearly grey, and reddish. It is dull, adheres to the tongue, and yields a strong argillaceous odour. Its streak is paler than the surface, structure earthy; it is soft; fracture, slaty.
Localities In New South Wales it is found on
Mount Victoria; also between that locality and Mount King George; on the Middle and Northern Hunter, Campbell and Abernethy rivers; to the south of Arthursleigh, north of Modbury, east of Gidley; at Lake Omeo, and to the north and south of Gipps Land.
In Van Diemen's Land it appears between the mouths of the Great and Little Forrester rivers; at Emu Bay; Rocky Cape and Montague rivers.
Their inclination is irregular; their thickness does not exceed 25 feet.
Var. 2. Claystone. (Jameson.)
This assumes a variety of colours; chiefly yellowish white, lead grey, sky blue, and brick red. The stone is dull, massive, semi-hard, slightly adherent to the the tongue; it yields an argillaceous odour; the streak is similar; fracture is splintery, uneven, or, in some cases, conchoidal.
Localities In New South Wales it is found to the
west of Arthursleigh; in the vale of the Clwyd; at Coyal; to the north-east of the Hunter; and at Lake George.
In Van Diemen's Land it occurs at St. Patrick's Head; at Lake Tomb, Ben Lomond; between Tamar and Rubicon rivers; on the river Forth; at the Western Bluff and the sources of the river Nive.
Var. 3. Aluminous Slate.
Colour, greyish black, sometimes verging on iron black; external and longitudinal fracture shining at times with a metallic lustre; structure slaty, with layers straight or curved. It is unctuous and brittle; fracture somewhat laminated.
Localities.—In New South Wales it is found at Walerowang, also at Balangola and Arthursleigh. In Van Diemen's Land it appears at Emu Bay, and at Cape Grimm.
A somewhat arenaceous compound, of a yellowish, reddish, or bluish colour; composed of quartz, with occasionally mica and glassy felspar, cemented by an indurated argillaceous or felspathic paste. Its structure varies from a coarse sandstone to a finely comminuted and compact mass, seldom possessing a distinct cleavage, or exhibiting a slaty appearance. Its external and internal aspects differ very little; generally it adheres to the tongue, and exhales an argillaceous odour.
Localities.—In New South Wales it is found at Port Stephen West; at Booral; on the Upper and Lower Hunter; between Bathurst and Frederick Valley; at Lake George, and on the Shoalhaven. In all these localities its geological position is between the uppermost mineral masses of the first epoch and the lowermost sedimentary deposits of the second.
In Van Diemen's Land, greywacke extends over larger tracts of country. It is found on the river Bobiala; at Cape Portland; Mount Cameron, where it is associated with eurite and clay slates; at St. Patrick's Head, where it lies between siliceous slate and limestone; at the confluence of the Tyne and South Esk, where it is associated with siliceous slate and clay slate; on the south side of Ben Lomond, and the west arm of the Tamar, connected with the granular limestone of those localities; at the eastern foot of the Western Tier, between breccia and clay slate; at the source of the Mve, along with clay slates and limestone; and between Emu Bay and Cape Grimm, constantly associated with siliceous slates, granular quartz rock, and clay slates.
General Remarks upon the Second Epoch.
The geological and mineralogical discrepancies which will be observed to exist among the sedimentary rocks above described, great as they appear, are nevertheless such as might have been inferred from an examination of the form of the first upheaved land, which served as a ground-work for the further enlargement of the geological edifice.
The form of this land has given rise to eddies and currents, which, judging by what we see in the present day in Bass's Straits, may have either powerfully assisted the general agencies which effect the abrasion, comminution, and dissemination of materials, and the reconstruction of rocks, or may have equally tended to counteract the effect of such. Thus the difference between two localities, arising either from a difference in the number or mineral character of the members of the series, or the abundance or paucity of the characteristic fossils, becomes only an evidence that one locality has been more favourably situated for the accumulation of certain geological records than another.
The organic remains which have distinguished this epoch had been found, by Mr. Lonsdale and Mr. Morris, to possess great analogies to those of the Palaeozoic series. How far this analogy is borne out by the specific character of the Australian fossils, will be fully discussed in the able paper which these two eminent naturalists have furnished to the Zoological Section of this volume.
As regards the crystalline eruptive rocks, which have been noticed in more than one locality, partly as being merely associated with stratified rocks, partly as immediate causes of their dislocation, convulsed and confused groups as they present, their eruptions may nevertheless be referred to certain distinct and distant periods, and may be classed chronologically by means of the geognostic evidences furnished by the sedimentary rocks with which they are in contact. Thus the eruption of greenstone in the Liverpool, Coyal, and Honeysuckle ranges, those of the basalt along the spur which is crowned by Mount King George, and the eruption of both these rocks in the "Westmoreland country, may be assigned to the period intermediate between the formation of the siliceous and aluminous detrital masses, and that of the aluminous and calcareous fossiliferous and non-fossiliferous sedimentary deposits. In all these three cases the siliceous and aluminous rocks, the lowermost of the series, were in position highly inclined, while those which follow are horizontal, or nearly so.
To this period belong also the most striking eruptions of greenstone in Van Diemen's Land, namely, those by which the completion of the actual dividing range from St. Patrick's Head down to Table Mount was effected, and those which formed the elevations of Ben Lomond, Ben Nevis, Mount Horror, Mount Barrow, Mount Direction, and Mount George. To this same period may likewise be referred the greenstone and basaltic spur running between Western Bluff and Asbestos Hills, and that which shoots out from St. Valentine's Peak to Mount Cameron West, with all those lateral branches that contorted the clayslate system between Emu Bay and Cape Grimm. In all these localities of Van Diemen's Land, as in the preceding ones of New South Wales, the lowermost arenaceous and aluminous detrital masses are the only ones which are disturbed, and which have a highly inclined dip.
Again, the date of the eruption of porphyries and greenstone at Port Stephen must have been at the period at which the deposition of the slaty argillocalcareous fossiliferous rock terminates, and before that at which the formation of the coarse sandstone with conularice and terabratulce began. Coeval with this porphyritic eruption may be classed the eruption of porphyries at Barber's Creek, and that of porphyries, greenstones, and basalts at Mount Canoblas, Boree, Molong, Narrigell, Wellington, and the west of Yass Plains. In Van Diemen's Land, contemporaneously with these eruptions, took place that which produced the spur that shoots off from Table Mount, and is crowned by Mount Dromedary. In all these localities we see every member of the series, including the slaty fossiliferous, greatly disturbed.
Next after this period we can trace the record of