Geological and other Reports
Terraces and Raised Beaches
Terraces and Raised Beaches.
Terraces and raised beaches are a very prominent feature in the Geology in this Province.
It appears to me that during the “drift” period, this Province and perhaps the whole of the North Island, stood at a level of 1000 feet, a little more or less, below its present height.
At about 1000 feet, gravel terraces are found,* and also at about 400. 150 to 200, 15 and 4 to 9 feet. Between many of these larger terraces, smaller ones may be perceived.
That these terraces generally mark successive rises of the land is probable, although the evidence of fossils is in general wanting† (and this may indicate a glacial origin, for many of the terraces instead). I have, however, seen in the Wairarapa one terrace at least, which in a few years will be indistinguishable from the others, and which was caused by a “fault” during the earthquake of 1855.
At Terawiti, Oriental Bay, and elsewhere round the coast, there is evidence of a very marked sea beach, waterworn, and the rocks bored by pholas, at about 15 feet above the present high water mark. It seems almost superfluous to mention the marks of the well known rise of the land in 1855, of from 4 to 9 feet.
At the time of the deposition of the “drift” gravel, the tertiary basin of the West Coast, must have presented a series of unbroken, level, or slightly inclined terraces, beneath the sea, otherwise, the narrow valleys which now exist, would have been filled up by the “drift” in angular deposits.
The “drift” of the Mungarua hill, and others of similar character, probably mark the sites of ancient glaciers.
Within the limits of Wellington itself, there are considerable deposits of gravels and clays resting on the old rocks and containing plant impressions. At Burnham Water there are strata of gravel and sand, containing struthiolaria, ostrea, pecten, turritella, &c., at a height of about 10 feet above high water mark, and also beds of peat covered by sand, and at Makara there is a fossiliferous patch, probably marking an old sea beach. All these would appear to be “recent.”
Since writing the above I have received Mr. W. B. Clarke's report of January 5th, 1864, of which I enclose a copy, not only to show the progress of the argument as to the age of our Palæozoic rocks and the difficulties which surround the question, but also to point out to you and to the inhabitants of Wellington, how much trouble Mr. Clarke has taken, and how much interest he has shewn, in the advancement of the knowledge of the geology of our province, and, I may state, that this report only embodies a small part of the work which he has performed, for I have been in constant correspondence with him ever since the commencement of the geological survey, and have received from him the most steady and zealous assistance.
My first impression was, on reading this last report, that I should have to modify and alter all that I had written previously concerning the Palæozoic rocks; but, on second thoughts, I have decided to leave my original report with a few alterations only, and to add a few observations on Mr. Clarke's views, as expressed in this last communication. As the argument as to the age of our old rocks will probably sway backwards and forwards for some time to come, until more distinctive fossils are found, I believe this plan will be most conducive to show what results have been arrived at, and how we have reached them.
* Possibly several hundred feet higher may be included.
The main points to be determined by me after a consideration of Mr. Clarke's last report, are as follows:—
|1st.||Does our main range consist of one group of rocks only, or of more than one?|
|2nd.||Of what age are these rocks, whether of one or more groups?|
In reply to this, I consider that Mr. Clarke's previous decision, in which he establishes the carbonaceous character of the rocks at a great variety of points, is almost conclusive as to these ranges consisting of one group only. I have already stated my views on this head and also with regard to the supposed Mezozoic rocks and therefore I need not repeat them. I can see no appearance of unconformability among the old rocks, they seem to be all equally thrown up at high angles, but the numerous dislocations, bends, and faults render it difficult to speak with certainty and I will not deny the possibility of there being two groups of rocks within the ranges.
The supposed Phyllotheca of Porirua, as also the Theca, or Dentalium of Belmont, may soon assist us to resolve this question.
With regard to age, although I have been tempted in the direction of the Carboniferous, yet, I must now confess, that the balance of evidence is in favour of older rocks. The supposed coal has appeared all to resolve itself into graphite, for even No. 55, from the Ruamahunga gorge, which has a strong appearance of coaly structure, I know positively will not burn, and will probably prove to be a graphite like the rest.
The relation of similar graphite to the auriferous lodes of “St. Arnaud” may perhaps tempt to further careful examinations in such places as the Otaki river, where the “black mineral” is in abundance.
Mr. Clarke's theory as to the deposition of the graphite from water is a probable view, in some cases at least, for there are reasons to suppose that hot springs have played a considerable part, both in the main range and on the East Coast; but we must also consider that the “plant beds” of Porirua and of Oriental Bay, and also some obscure impressions on the Otaki river, show the presence of plants, which appear to have been imbedded in the usual manner and therefore the carbon there was not derived from infiltration.
It may appear that the result arrived at as to the age of our Palæozoic rocks is still very indefinite and that I might have been prepared with a more direct statement; but, if you consider the evidence which is now before us, you will draw the inference that our difficulties have probably arisen from the transmuted character of the rocks, and the consequent destruction of distinctive fossils.
This difficulty may permanently prevent our arriving at any definite result, but, as I have been able to find some organisms, however obscure, which help to show in what direction to search, there is every reason to hope, that as the country is opened, and the rocks broken into for road-making and other purposes, characteristic fossils will be brought to light.
To be enabled step by step to gain a correct knowledge of the age of our rocks, it is almost essential that we should have a properly regulated Museum, under a Curator, otherwise comparison is impossible, the results of observations are lost, and each fresh enquirer has to begin anew.
In connection with the argument as to the granitic character of the rock, marked No. 3, Upper Hutt, I subjoin a list of the specific gravities of some of our rocks as weighed by me, warning you, at the same time, that I was not in the possession of a balance of great nicety.
|Slate near Featherston||2.77|
|Slate near Featherston||2.63|
|Ferruginous quartz, Waikanae||2.7|
|Quartz, Mungaroa hill||2.4|
|Quartz, Mungaroa hill||2.55|
|Serpentinous Slate, Otaki||2.73|
|Quartz, Pitoni road||2.62|
|Jasperoid Rock, Rimutaka||2.71|
|Sandstone, of Waikanae||2.52|
|Soft Clay Stone, Mungaroa||2.22|
|Soft Clay Stone, Belmont Hill||2.29|
|Carbonaceous Rock, Porirua||2.45|
|Serpentine, Mungaroa hill||2.73|
|Green effeiveseent pyritous rock, Petoni road||2.61|
The above list would seem to show that the disputed granite (No. 3) is of no page 11 greater specific gravity than so no other rocks of the range; consequently the argumenent founded on the specific gravity is weakened.
I cannot say that I have any faith in Gold being found in this rock in payable quantity, but undoubtedly it should be tried. “Diggings” need not be expected in its neighbourhood, if the diallage contains Gold it will be in a state of extreme fineness.
This rock of Waihekino traverses calcareous rocks which I suppose to be “sacondary,” and if I am right in this view the chances for gold are not encouraging.
Since I have framed this report I have visited the Waikato country, and I there see unmistakeable evidence of an era during which the central volcanoes have emitted an enormous quantity of pumice and volcanic ashes, which, on being washed down from the interior, have covered up the country to a considerable depth, burying and destroying an ancient forest.
I have some reasons for supposing that this era was one of submergence, but those which I can perceive against this view are more cogent, and I think the action of rain and rivers sufficient to account for the distribution of the materials.
Indeed, as pumice floats in water, it would be difficult to show how it could be deposited from the sea at all, unless heaped up upon the shore.
I may also state that my observations in the Waikato lead me to suppose it probable, that the tertiary coal field of Whanganui is a continuation of that of the former district, although, I am bound to say, the associated rocks do not appear, on a cursory view, to bear the same lithological character.
During last winter I made drawings of all the tertiary fossils which I had collected, with an expectation of having their species determined in time for this report.
This however I have not been able to get accomplished, but I hope to receive information, concerning them, which I may forward to you at a future time.
Dr. Haast informs me that Zittel has divided the New Zealand tertiaries into two main sub-divisions.
I suppose both of these to be represented in the Province of Wellington, but until I have been informed as to the species of our fossils, it would be premature to lay down definite conclusions; the large cucullæa however, associated with the “Blue clay,” appears to indicate the older tertiaries, overlying the brown coal beds; while the more recent tertiary beds are largely developed on both sides of the Province.
Mr. Clarke has forwarded all my Palæozoic organisms, or supposed organisms, to England, for examination, so that by and bye we may hear of them again.
In conclusion, I think I may claim to have advanced the knowledge of our rocks, as far as could have been expected, considering the obscurity which previously hung over them, and the scarcity of fossils. I also think it may be shown that I have saved the Province some outlay, both in what it must have paid for an imported Geologist, and in avoiding the employment of a “Staff,” when it could not have been satisfactorily made use of.
I have to thank you and the Provincial Council of Wellington for your support in a highly interesting investigation.
I have to thank my old friend, the Rev. W. B. Clarke, for the very great trouble which he has taken in assisting me, and for which the Province also should be grateful.
From Dr. Julius Haast, the Government Geologist to the Canterbury Province, I have always received prompt and intelligent assistance, and he has now kindly undertaken to watch the progress of the lithographing of the Geological map of the Province, at Christchurch. My thanks are also due to Mr. Brough Smyth, Secretary to the Mining Department at Melbourne, and from Dr. Lauder Lindsay, I have received valuable information.
Last, but not least, Mr. Walter Mantell's services were always at my disposal, for the investigation of minerals, or for the determination of fossils.
I have the honor to be, Sir,
* Six miles South of Flat Point.