It is to be remarked further that plant impressions of a black carbonaceous appearance are found through the sandstone, showing an occasional growth of plants on the sandy surface. At any rate, in the presence of such plant remains, often with roots, we have no other evidence but that of a terrestrial vegetation, and are not justified in having recourse to any other hypothesis. The plant remains are not aquatic; and there are strong reasons for supposing that Thinnfeldia was a Conifer allied to Phyllocladus (our Celerytopped Pine), and not a fern.

JOINTS.-It will be remarked that the shales are conspicuously jointed with a uniform direction. I have found that the jointing is always at right angles to the strike of the dykes of diorite, basaltic rock and trap, and which so numerously intersect the formation. We may regard these dykes as so many wedges of rock inserted in the mass, and of course increasing the lateral pressure. This would be quite sufficient to account for the joints, which are obviously connected in direction with the volcanic intrusions.

DYKES.-All around the Nepean Valley dykes are common. It is remarkable that they have disturbed the surface but little, and the Hawkesbury sandstone is only tilted a few inches at each side, the elevation extending a few yards in a horizontal direction. In the immediate vicinity of the dykes the sandstone is metamorphosed into a hard siliceous rock, sometimes not distinguishable from the injected material. This is easily understood if we remember that the sands are felspathic, and probably altered back again by heat into the form of the granitoid rock from which they were originally derived. The surface portions of both dykes and matrix are much altered by water, and these are the only portions I have been able to examine.

Shales on Sydney sandstones. In a few places around Sydney shales are found in somewhat thicker beds than the shales near Campbelltown, but they are different in character, and far less carbonaceous. They are at least 100 feet lower than any of those round the valley of the Nepean.

That they are of the same character as the shales in other portions of the formation can be seen from the following section obtained in a boring at the Oaks Brickfield, near Neutral Bay :—

Height above the sea, about 150 feet.

The shale here is somewhat of the same composition as elsewhere, but less micaceous, and with considerably less carbonaceous

matter.

It is a very pure fire-clay, with so little iron in it as to render it very valuable for fire-resisting purposes.

In the boring for coal at Moore Park by the Diamond Drill Co., at 20 feet above the sea, the section gave 143 feet loose sand, 900 feet false-bedded sandstone with occasional shaly seams, but no record of the amount of shale was preserved, as the cores themselves were kept for exhibition at the Garden Palace, and where they were destroyed by fire. A band of ironstone 263 feet thick was found at the base of the Hawkesbury rocks, and then the coal measures were reached and bored for 550 feet without meeting coal.

.

Economical value of the Shales.-Up to this no great use has been made of the shales, but there can be no doubt that they are of considerable commercial value. For the manufacture of pottery, certain patches of shale would be found to answer as well as any in the world. It consists of a true silicate of alumina, finely levigated and mixed together, with very little iron or other minerals. The alumina predominates, and this is to the advantage of the ware. Generally speaking, the more the alumina the harder the ware, and the more silica the softer the ware; the latter is less dense and bears less heat than the former. Bricks have been made from the shale from a very early date in the Colony. They are largely made from the shale at Lithgow; at Waterloo, by Messrs. Goodlet & Smith; and at the Oaks' brick-works, at Neutral Bay, and other places. In the latter locality the shale is particularly free from iron and grit and contains more alumina, so that a very white brick comes from the kiln. It is very tough, and shows a colour and structure which manifests how easily fine pottery could be made of the same substance; in fact it seems a pity to use such material for bricks. I am told that a high price is paid for fire-bricks to use with these, the builders evidently not being aware that no finer fire-brick could be found than that manufactured from this clay. No doubt it will be largely used and its value appreciated before long: the only matter of regret is that near Sydney the supply of shale is somewhat limited.

For all the reasons previously given, I think that the term “Waianamatta formation" should be abandoned by geologists, as not being represented by any distinct group of rocks.

I have to express my thanks to Mr. Keele and Mr. McKinney, and other assistant engineers, for their kindness and attention to me during these investigations, especially in determining all the levels and making the measurements of strata. All these gentlemen, as assistant engineers in the Waterworks Department, were thoroughly acquainted with the locality, and showed me, during many days' research, every point of interest and importance.

Further remarks on Australian Strophalosiæ; and description of a new species of Aucella, from the Cretaceous Rocks of North-east Australia.

By R. ETHERIDGE, Junr., F.G.S.

[Read before the Royal Society of N. S. W., 4 July, 1883.]

1.-NOTE ON AUSTRALIAN STROPHALOSIÆ.
Genus STROPHALOSIA. King, 1844.
(Annals Nat. Hist., 1844, xviii. p. 28.)

Strophalosia Gerardi. King.

S. Gerardi. King, Annals Nat. Hist., 1846, xviii, p. 93. S. Gerardi. King, Mon. Permian Foss. England, 1850, p. 96, t. 19, f. 6 & 7.

S. Gerardi. Etheridge Junr., Proc. R. Phys. Soc., Edinburgh, 1879-80, p. 294, t. 12, f. 34-37, t. 13, f. 38. [For general synonomy.]

Obs. The specific characters of this species have already been given elsewhere, and, with the exception of the degree of concavity of the dorsal valve, little or no alteration is needed. The description referred to was drawn up from the type specimen in the cabinet of Prof. W. King, kindly lent to me for the purpose, with other specimens, which I conceived belonged to this species, forwarded from Queensland by Mr. R. L. Jack. The shells now before me, obtained by Prof. Liversidge, F.R.S., will I think set at rest the question of the occurrence of this Himalayan species in Australian rocks, so far as one can judge from the meagre material at present in this country from the typical locality. The specimens sent by Prof. Liversidge show that the concavity of the dorsal valve varies to some extent in different individuals, from the deeply concave condition formerly described by me to the semiconcave form now referred to. The length of the hinge line is also very variable, long in some examples, short in others, although, as before stated, it never extends the whole width of the shell.

Furthermore, the examples of this species now under consideration give us an insight into the internal character of the ventral valve, but unfortunately not of the dorsal one. casts of these interiors show the deep blunt umbonal cavity of the

Wax

beak, a reduction in the size, and a modification in the form of the teeth, entire absence of the imprint of the adductor muscles, smaller size of the cardinal muscle scars, and the deeply corrugated nature of the front interior portions of the valves. On the exterior of these specimens the lamella of growth and short projecting spine bases are exceedingly well shown.

When my former description of the Australian Strophalosiæ was written, I defined three species. The first of these was Productus Clarkei, Etheridge; the second, a form to which I gave the name of S. Jukesii; whilst the third was King's S. Gerardi. These I described fully, according to the material then at my disposal, and made the following remarks :-" It would not surprise me if, eventually, we have to unite the shells now described as Strophalosia Clarkei, Eth., S. Gerardi, King? and S. Jukesii, Eth. jun., in one variable species, although, as I have before said, such a proceeding would be premature, as the material to hand is not sufficient in itself."1 Since the above was written I have not seen any evidence to justify a union of S. Clarkei with S. Gerardi. On the contrary, Prof. Liversidge's specimens, from the structure of the ventral valve, incline my opinion the other way; but as regards S. Gerardi and S. Jukesii the matter is not so clear, for these Darr River shells externally appear to unite the two species. The internal structure of the ventral valve of S. Gerardi is known to us, but not that of S. Jukesii; and similarly we are acquainted with that of the dorsal valve of the latter, but not of the former. A very decided difference is indicated by the prominent teeth which must have existed in the ventral valve of S. Jukesii, and of which there is no trace in the Darr shells I have referred to S. Gerardi. The present notes can only be looked upon as a further contribution to the solution of this interesting question, which must still remain an open one.

Loc.-Darr River.

FOSSILS FROM THE CRETACEOUS ROCKS OF N.-E.

AUSTRALIA.

Prof. Liversidge has also forwarded a few fossils from the cretaceous rocks of N. E. Australia. The specimens appear, from their external appearance, to be portions of boulders (or rounded blocks), and comprise Bivalves and Cephalopoda only.

The Bivalves consist of two species of Inoceramus, an Aucella, and possibly a Monotis, or allied genus.

The great variability of the shells forming the genus Inoceramus renders it very difficult to decide on the specific identity of its

1 Proc. R. Phys. Soc., Edinb., 1879-80, p. 309.