Geological and other Reports
Upper Hutt (Granite?)
No. 3. I can find no waterworn particle in this rock, and I have very carefully examined all the specimens with various microsopic powers in that view. The appearance of the rock is that of dykes or veins which often traverse granite, and to one of these I referred it at first. That it is bedded, I doubt, but it is jointed in several places and traversed by threads of segregated matter, parallel with one or other of them. Its chief elements are crystalline particles of felspar, with some minute traces of glassy felspar, quartz, sometimes crystalline, sometimes basic, with but little mica in proportion to the other, and that is silvery. There are also small points which look like hornblende. I am quite satisfied in my own mind that it is an igneous rock, putting on the character of euritic granite. Dr. Haast mentions a sedimentary rock, which has been taken for granite in the Eastern part of the Western mountains of the Nelson Province, and he satisfied himself it was so after much research. But he must in that case have found unmistakeable proofs of sedimentary origin; there is not one single waterworn particle that I can detect: if you can find any that will leave the rock under the head of hardened, regenerated, granitic detritus,* but such detritus would betray its secondary composition. The rock is much decomposed though very hard.
P.S.—As a further test I have to-day (6th January), taken the Specific Gravity which comes out 2.70. Now compare this with the following hard rocks and you will see its character.
|Baked white grit, columnar, compact, Bondi, N.S.W.||2.37||By W. B. Clarke|
|Baked white grit, columnar, compact, Wattle Swamp||2.45|
|Baked white grit, columnar, compact, Pyrmont Stone||2.331|
|Baked cherty columnar sandstone, Sturt's Creek, brought by Gregory, N.W. Australia||2.338|
|Granite||2.73||Mean||By Professor Haughton.|
Piloni Road, Otaki River, Rimutaka, Terawiti, Wai-nui-o-mata, Otaki River.
Nos. 42. 44, 54, 52, 72, 81, 87. These rocks are partly siliceous, partly calcareous, or slaty with quartz and lime, and have very much the appearance of the walls of mineral veins.
They are all more or less covered, or interlaminated, or mixed up with a black mineral which puts on either a powdery sooty aspect, or a compact hard glossy one, (not improbably the result of friction like black lead polish) especially on the surface. No 54 is covered with it in such a way as to lead to an idea that the mineral was sometimes spread by water over broken surfaces of the calcareous rock. This remark also applies to No. 72, One of No. 42 looks more like a carbonaceous shale.
No. 52 shows the substance diffused between all the cracks in the rock. So in No. 81 one of these specimens is a quartz vein so covered. Another of No. 42 do. Another of No. 81 exhibits marks like those of slickensides, indicating motions of surfaces against each other, and the substance in question shows in places (in the harder varieties as in those of No. 54), just such markings as are found under like conditions, as if it had infilled the hollows of a scratched rock, or had contracted on drying and hardening. Again in No. 42, we find patches of iron ochre in combination with the black mineral, as if a ferruginous spring had coated it. In No. 87, the thin surfaces of the plates and joints of a black slate or shale are likewise coated by a shining black wash of the same.
* Note.—After a further examination I believe we must accept this latter alternative.—J.C.C.
Now what is this substance?* There is not a trace of Manganese Its composition is silicate of alumina, hydrated iron carbonaceous matter, and a trace of lime.
Whether the carbonaceous matter has been derived from water passing through coal is doubtful, much of the stuff is like coal, soot, or smut, as you will perceive if you examine the water after washing it. But the composition above given, which has been carefully arrived at, is not so much that of ordinary coal, as that of a kind of Graphite, which you know is a mineral (though related to coal in some way) more transmuted than anthracite, and is chiefly confined to rocks much older than those of the coal formation† Earthy graphite is by no means uncommon in the Southern Hemisphere, and there are abundant proofs of the existence of carbonaceous matter in the Silurian formation.
I have received a mineral not unlike some portions of yours, from Tasmania and have found it in New South Wales, and in my collections from New Caledonia, I am able also to tell you that this very substance, though softer, and occasionally with minute traces of copper, is found coating the sides of the auriferous and argentiferous veins of “St. Arnaud” in Victoria, as I am informed by Mr. Ulrich, of the Geological Survey of that Colony, who has sent me a sample of it, of which I include a few particles.
With these slight aids, perhaps you may be able to detect the relation of this mineral with the older Palæozoic rocks of your Province, if not with any independent system of coal beds. Whatever may be the result, I am bound to say that in the collection now before me, I see not more than the resemblance I have already mentioned to beds of coal or to the rocks usually associated with such. To these remarks belongs the examination of the next specimen.
No. 97. ‡ A fine sedimentary highly calcareous rock (calcareous sandstone) of grey colour, and chiefly silicious origin, coated and patched with carbonaceous matter of similar kind. N.B.—I do not forget that a speci-
55 men No. 55, Ruamahunga gorge, on a former occasion, exhibited what I cannot help thinking is a trace of coal altered so as to wear the appearance of anthracite, or graphite, some portions exhibiting interlaminations of our present mineral, which may therefore really be connected with coal of some age or other.]
In the Porirua plant beds you frequently see the same.
The general conclusion must be, that however derived, the carbonaceous substances with the rocks holding them have been highly transmuted, an opinion confirmed by the existence of jasperoid and cherty, as well as hardened limestone rocks in the midst of these ranges. This is further confirmed by the undoubted evidences new produced of direct igneous action.
* Note.—The carbonacerous matter in the thick shining crust amounts to about 2.3 per cent. As tihe Specific Gravity is very high 2.8, and the hardness of that portion about 5, it is quite a new combnation.
† N,B.—Professor Rogers has shewn that the Anthracites of the Appalachian chain lie at the bottom of the coal series, just where the igneous rocks would prouce the necessary metamorphic action.
‡ It is doubtful whether this rock belongs to the main group of the Palæozoic rocks.—J. C. C.
No. 37. The cast of a portion of the plant in this specimen resembles very much the stem of Phyllotheca, but it may be that of a fern. If the former it would bring the deposit near to one of our New South Wales beds in the coal series, probably the upper. Dr. Hector writes me word, that he recognized on the West Coast, Otago Province, beds very similar to those of Western Port in Victoria, which I consider equivalent to our upper coal beds. There is something very like your plant beds not far from Port de France, where the Mezozoic rocks lie at the base of the great serpentine ranges.
Ko a rai tea, Otaki River.
Eklogite,—Not a true granite. (This is certainly not in situ, W.B.C.)†
Top ridge of Tararua.
Would have been called greywacke some years ago. It contains felspar and mica, with quartz veins.
Felspathic trap. It is probably a porphyritic greenstone.
Tabular quartz with iron. There is abundance of this on the Hanging Rock Gold Fields, N. S. W. It occurs close to serpentine. I believe it to be the result of hot springs.
Highly calcareous trap. May be an altered ash. The imbedded crystals are too small to test.
Iron pyrites in a trap, or metamorphic state. Character of rock indistinct.
South of Flat Point.
Diallage or Bronzite in calcareous greenstone, full of iron pyrites, and not impossible with gold in minute quantity. (By all means get enough of this to test.)
Kahumengi, East Coast.
Boulder of Trachytic Porphery, containing much iron pyrites
Additional Notes on the Graphite from Van Dieman's Land.
Pure Plumbago consists of:—
|90.9||×||9.1.||= 100.||(According to Berthollett)|
|Graphite of Plusier:—||Carb. 23 }|
|Iron 2 }||100|
|Al. 37 }|
|Si. 38 }|
Now, if Al. and Si. be considered impurities the proportion of Carb. to Ir. will be 91.3 to 8.7, a curious relation. I believe this specimen contains much less. 98 grains of it were burned for 6 or 7 hours, so that nearly all the carbon was destroyed. It then weighed 89 gr.
|The mineral contained, Carb.||9.081|
|Iron, Alb. and Si.||90.919|
Some of the burned mineral was macerated in diluted sulphuric acid and Carb. Soda, and threw down a brownish precipitate which appears to be Al. and Iron.
Now examine yours and that together. Does it not resemble the Otaki specimens.
* N.B.—Theca belongs both to Carboniferous and Silurian formations. Dentalium goes as low as Carboniferous.
† Most certainly it is.—J.C.C.
Note on Plumbagenous Coal in America.
(Which will enable you to determine how little, or how much weight belongs to Silurian speculation.)
From Mansfield in Mass. to Newport in Rhode Island, the whole of the coal is altered, so as to appear as Graphite or Plumbago. In Fortsmouth, Rhode Island, at one out-crop, the coal is light, spongy or cellular. It is sold as Plumbago under the name of British Lustre. Asbestos occurs abundantly in the shales near the coal: and that, as well as the shales, are traversed there and in Massachusetts by quartz veins.
Now in this region, the fossils are those of the ordinary coal formation, and thus Dr. McCulloch says, (Vol. II., page 297), coal of secondary origin: containing vegetable remains is converted into plumbago by the influence of trap, as coal is daily in the iron furnaces.
Formerly anthracite in Ireland was confidently spoken of by distinguished Geologists in transition clay slate intermixed with considerable beds of quartz. Now it is universally admitted, that, that entire coal field is of no older date, than the regular bituminous coal fields elsewhere. This was the case also with the Western part of the South Wales coal basin. It was then called “Grauwacke.”
Again, Sir C. Lyell says the rocks which contain the plumbaginous anthracite of Worcester (Mass.) are merely altered rocks, the grits and shales of the coal measures have been thus changed to quartzite, clay slate and mica schist and the anthracite into that state of carbon which is called plumbago or graphite. † Mr. Hall tells us that in one part of South Wales, bituminous coal exists at the top of the same series of beds with anthracite at the bottom,* and without igneous rocks. He thinks internal temperature sufficient alone.
Reading the above in connexion with others from my letters you will see the possibility of a coal field once in existence with you. It is for you to weigh how far the actual evidence goes, if these notes help you I shall be glad.
† See Q. J. S., May, 1845.