Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/388

262 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. In the New-South-Wales Catalogue of the International Exhibition, T. Dalton, Esq., remarks, on the Rocky-River district, that vegetable remains were found in a silicified state amongst the lowest strata of sand, resting upon the granites, beneath the basalt on all parts of this gold-field. Respecting the clays that intervene between the basalts and drifts of quartzose sand, he says, "In some cases these clays alternate with sand-drifts. There is no sheet or stratum of clay extending over the entire Flat at any given depth beneath the basalts ; on the contrary, they vary in colour and thickness in almost every claim ; on the southern part of the Flat, buff, black, and pure white predominate. All these sands and clays appear to have been derived from the decomposition of the neighbouring granites and their quartz-veins."

" Sydney Flat is a depression situated just beneath the basaltic plains that form the summit of the main range. It is bounded on the south by Mount Jones, and on the north by Dogherty's Hill. The granite under Mount Jones crosses Sydney Flat, and, passing under Dogherty's Hill, maintains a general level, with the exception of bars trending north or north-east, the channels between which are full of now soft granite, which falls to pieces at the touch."

I have already pointed out* that the surface of the Australian continent appears to have been subject to great denudation, the Sydney Flat district being another evidence of the fact, in which thick drifts and dense conglomerates have to be passed through, with occasional beds of clay or marl, to reach the auriferous deposits of the granitic basin below ; whilst these are, in their turn, covered up by basalts of probably Tertiary or Posttertiary age.

It would appear, at first view, that drifts of such great thickness, and covering so large an area, must have been attended by phenomena altogether unfavourable to the preservation of the more delicate organisms of the period when they were deposited ; but, on the contrary, it will be seen that not only the vegetation but the most fragile insect-life of the period may be found in the marls and clays intercalated with the auriferous drifts of the Rocky-River district. It is probable from this that the drifts have been deposited at varying intervals, and that there have been periods of repose within which the laminated marls and clays, which are associated with them, were slowly accumulated in the basins in which they are now found, whilst often these may have again been partially denuded by the recurrence of the phenomena which produced the drifts above them, and with which they are associated.

On proceeding to examine the piece of laminated marl, I detected the presence of vegetable remains, and soon succeeded in opening up a tolerably perfect leaf, though wanting its apex, of some dicotyledonous plant. This was followed by a second leaf, belonging to the same order, but to a different plant ; whilst a third genus is shown by the upper part of a flat narrow leaf, evidently allied to the Coniferae. The last appears to be abundant, as three or four examples were present, one or two of which were sufficiently well


 * Vide supra, p. 233.