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The Pamphlet Collection of Sir Robert Stout: Volume 68

"Ancient Glacier Deposits

"Ancient Glacier Deposits.

"I have elsewhere* given my reasons for supposing that the greatest

* "Transactions New Zealand Institute," v. p. 384.

page 14 extension of our ancient glaciers took place during the intervals between the Pareora and Wanganui formations, and in the next two sections I shall bring forward the additional evidence bearing on the question that I have collected during my survey of Otago. Of course, as glaciers still exist in our mountains, our glacier deposits must range in age from the most ancient period of their greatest extension up to the present times; and in this place I only propose to describe the more ancient deposits This, however, is easily done, for, with the exception of the Blue Spar already described, I as yet only know of two morainic deposits in the whole province that I am inclined to refer to this period. The first of these immense accumulations of clay and angular blocks of schist of all sizes that is found on the eastern side of the Taieri Plain, extending from the Taieri River nearly to Otakia, a distance of about three miles. This deposit is a confused mass of quite angular fragments of schist-some of them of large size and composed of mica schist with quarts laminæ, which must have come either from the neighbourhood of Outran or down the Waipori River. They could not have come from Brighton on the sea-coast, as many of the blocks are considerably above the highest level of the mica schists there, and there is no conceivable agency by which they could have been brought from there. Consequently, although I could find no trace of striæ upon them, I have very little doubt but that they were placed in their present position by a glacier descending from the Lower Taieri and the Waipori River." *Hutton, page 62.
This places the eastern end of the glaciers quite close to the coast From a cursory inspection of the locality, I venture to express a doubt whether this deposit is not a small outlier such as might be brought down by an avalanche carrying forward part of a true moraine I have noticed similar evidence of glacial deposits on the western sided of the Taieri Plain where cuttings are made for the Otago Central, and it is possible that the ancient Taieri River was the bed of a large glacier, into which smaller glaciers flowed, cutting such deep channels as that known as the Deep Stream out of the solid rock. The Blue Spur is another example. Hutton says in his report on the Tuapeks District:—
"Seated on the top of the saddle that divides Monro's from Gabriel's Gully is a deep, cup-shaped hollow in the schist rocks, which has been filled up, much higher than the present lips of the cup, by gravels cemented into a hard blue conglomerate. This is the Blue Spur, famous for the immense quantities of gold that have been derived from it. On close inspection, this hollow is seen to have been an old mountain tarn with smooth polished sides, which have, however, now decomposed into blue clay to a variable depth of from two to six inches Although I could detect no striae on the sides of the hollow, I have no doubt but that it was excavated by a glacier. This old rock basin is filled up with beds of conglomerate that dip to the east, and, as a rule

* Note.—I pointed out to a settler that there would probably be gold in the neighbourhood, running over to Brighton, and he tells me this is so. It might pay for hydraulicing, and is worth prospecting.

page 15 the stones in the conglomerates get smaller towards the east, which, together with the direction of the dip, prove that the old tarn was filled up from the west. The conglomerates consist in great part of pebbles and sub-angular blocks of green quartzite and a dark purple jasperoid slate with quartz veins, which rocks do not exist nearer than the Tapanui Mountains, west of the Clutha River, south-east of Lawrence; also, several other patches of conglomerates are found at the Blue Lead, Waitahuna, at Manuka Creek, &c., all of which probably mark the position of an old valley which extended from the Tapanui Mountains through the Blue Spur to Kaitangata. No appearance of such a valley can, however, be seen at present, and its supposed course is now crossed at right angles by the Clutha, and by the Tuapeka and Waitahuna Rivers. Consequently, this old valley must date back to a time previous to the formation of the present rivers, and, as we have already seen that the Clutha received the drainage of the pliocene glaciers of Maniototo, ldaburn, and the Manuherikia, we must place the existence of the Blue Spur glacier during a still earlier upheaval—that is to say, we must refer it to the Eocene Period."

Hutton, page 93.

I shall only quote one more authority—Dr. Archibald Geikie, L.L.D., F.R.S., in his "Class Book on Geology," page 458:—"From this kind of evidence it has been ascertained that the whole of Northern Europe, amounting in all to probably not less than 770,000 square miles, was buried under one vast expanse of snow and ice. The ice-sheet was thickest in the north and west, whence it thinned away Southward and eastward. Upon Scandanavia it was not improbably between 6,000 and 7,000ft. thick. It has left its mark at heights of more than 3,000ft. in the Scottish Highlands, and over North-Western Scotland it was probably not less than 5,000ft. thick. Where it abutted upon the range of the Hartz Mountains, it appears to have been still not far short of 1500ft. in thickness."

It is supposed that there are at least two distinct periods of glaciation, and one writer suggests that during the great Glacial Period the sea, by reason of the locking up of so large a quantity of moisture in the form of ice and snow over a large portion of the globe, was 2000 feet lower than its present level, which depressed the snow line to a similar extent. My learned friend, Mr. F. R. Chapman, has, however, produced some cogent arguments which cause me to doubt this, as for one thing the saltness of the sea would be so greatly increased by such a change that fishes could hardly exist. It is evident, too, that vast masses of rock have been cut down from the mountain tops by snow and ice, and their crests lowered. It is not too much, therefore, to say that at the beginning of the Ice Period our mountains were several thousand feet higher above the level of the sea than now, carrying a vast deal more snow on their crests and sides. Let any-one who is curious on the subject make a calculation of what quantity of material—say 1000 square miles, 2000ft. thick—would amount to in tons, and you will have some idea of the enormous quantity of solid rock which has been broken up and carried forward. A vast deal has turned into clay and sand and been carried out to sea, as over 90 per cent, of schist rock Would thus dissolve away; but still enormous quantities re- page 16 main in our valleys, old and new, river beds, old and new, terraces, and lake beds; and as the mountains from which these deposits come are auriferous, so must the detritus be. You have this in the form of large blocks, cement boulders, mullock, quartz, stones, and pebbles, and so on down to the black sand on our beaches. But there is evidence here in New Zealand, as there is at Home, of several advances and retrocession of the glaciers. There may within hundreds, or perhaps thousands of years have been periods of warmth, during which a vast melting of ice, and rush of floods of water towards the sea, would take place, and then periods of comparative quiet. The evidence of that state of things in New Zealand is to be found in the successive layers of lignite found at different depths. The vegetation from which these are formed must have had time and rest to grow to the thickness to which we know they have grown. The following bore taken at Clifton, near Invercargill illustrates this. There are six layers of lignite at different depths down to 105 feet, and an immense deposit of fine sand lower down, indicating a time of flood:—
Journal of Bore
Ft. In.
Surface 5 10
Lignite 4 6
Coarse Sand 1 4
Lignite 3 6
Clay 3 0
Sand 2 0
Lignite 1 4
Clay and Sand 2 0
Sand 4 6
Soft Lignite 0 6
Clay 2 0
Sand 4 0
Dark Clay 3 0
Sandy Clay 1 0
Coarse Sand 4 0
Lignite 2 6
Clay 3 9
White Clay 2 0
Sand 2 6
Fine Cl. y 2 4
Black Sand 4 0
Clay 2 0
Coarse Sand 10 0
Fine Sand 4 0
Sand and Clay 2 0
Sand 17 6
Sand and Cement 0
Sand and Fireclay 4 0
Sand 5 0
Lignite 2 9
Dark Clay 4 6
Sandy Clay 5 0
Sand 5 9
Fine Sand 48 6
Coarse Sand 3 0
Light Solid Clay 4 0
Hard Light Clay, with beds of sand 12 10
Sandstone and Fireclay in beds 4 8
Clay in beds of Sand-stone 26
Sandstone 7 5
Hard Clay 4 1

Now, the same state of things which would produce lignite seams, would produce leads of gold along the courses of streams, while during the heavier floods the stone would be more broken up that produced them, but the leads would be more concentrated at points where some hard bar or obstacle temporarily arrested the heavy rush of water and caught the gold in hollows. This, no doubt, was the case at Blue Spur. At Ross Flat, West Coast, six successive leads at different depths were found on sinking the main shaft down to 360 feet. I think, however, some mistakes have been made in predicting where leads would probably be found. No doubt, where a stream tipped its contents over into a lake, a catch would be established, and the free gold would not be carried far out towards the centre of the lake; but it page 17 must be remembered that besides the tree gold large quantities of slate and stones containing gold were carried forward, and gradually filled up the lake bed, and these, by their decay, have dropped their precious freight long after their deposit. Thus, as at Ross Flat, considerable quantities of gold may be found at successive levels over a large area of ground, and where a "face" can be got at a sufficient elevation to get a fall for the tailings, such ground will pay well for hydraulic sluicing on a large scale, as even a few grains to the load would leave a handsome result. There is room for much engineering skill in dealing with these various deposits, and much research by the practical geologist in determining the probable whereabouts of the best and most economically-worked ground. The young mining engineer of ability has a great future before him in this country, especially if he possesses, as he ought to possess, some knowledge of geology, mineralogy, and mechanics.

Generally speaking, Southland is a depression filled up in this way. Hence my belief that there is gold under your feet; where and how much can only be established by judicious and systematic prospecting and boring. But, generally, we may say that if the existing creeks and rivers contain gold, the terraces at their sides and the old river beds below will contain as much or more. There is here a field for a new department of the great science of geology. I may be permitted to coin, and call it "Glaciology." I admit that there is much for the geologist, and the mineralogist, and the chemist to do in other branches of historic and descriptive geology, but I think some men of ability among us should devote themselves specially to Glaciology, and I am sure its careful study would be fruitful of results, and principles knight be laid down of immense value to the hydraulic miner of the future. At present we can only deal with the poorer drifts by the use of immense quantities of water, and the creation of a vast quantity of waste material known as "sludge," which requires expensive channels I to carry it off. I am not at all certain that our present rough-and-ready system—which undoubtedly loses a great deal of gold—cannot be improved upon so as to economise water, and by mechanical appliances to keep the larger stones out of the channels—perhaps to crush them. The only limit at present to this class of mining is the water and the outlet fall, and Mr. Perry has, by his ingenious system, already overcome some of the difficulties of the latter by using water pressure to lift the materials to be washed to a considerable height. One good feature of hydraulic mining is that it is a steady industry, going on from year to year with few sensational results, but with a good return for capital and labour; and there is an immense field for it in Otago and parts of Southland. The use of thin steel plates for pipes is a great improvement.

And now I come to answer the question—