The Nature Column.

Digger (Invercargill RSA), Issue 31, 15 October 1920, Page 11

The Nature Column.

(By "Student.")

("Student" will be pleased to receive notes on any brantch of Natural History. Observations on birds, insects, plants, etc., will be>. equally welcome. lf using a pen-name, will correspondents please enclose real name and address. ) The late J. R. CuChbertson in the eighties read a paper before the Institute in Invercargill on our subterranean water supply. He stated there that the water bearing strata could be traced to the Dunsdale at a uniform depth. We have the same statement made to-day, i.e., "The continuous long line of auriferoua gravels tlirough which the water per"colates must exist without a break at an "average uniform depth underground "throughout the whole distance and on"ward in a north- easterly direction to the "region of its origin." This implies that the auriferous gravels were laid down by a river coming from the north-east. It also implies that the slope oi the country was much the same as it is- now. The only present day river which could have taken such a course is the Mataura. It might possibly have come through the site oi Invercargill.' But the heacl-waters of the Mataura in the not very far distant past were, according to Professor Marshall, the the head-waters of the Oreti River which flowed down the air gap at Eyre Creek through which the railway to Kingston now runs. Its present course is a new one almost from start to finish. Further none of the rivers of Southland, ihe Mataura included, take their rise in mountains containing quartz in sufficient quantity to account for the enormous deposits on the Southland Plains, includmg the water bearing strata under notice. Where then did all this gravel come from? A first-class geologist has said that the gravel from the town hores shows certain cliaracteristics. The quartz was in a massive form, and in schist country. In Stewart Island we find the schist and also quartz. The sea ig comparatively shallow down to the subantarctic islands and seems to indicate the existence of a continent now submerged. It is quite within the bounds of possibility that the river which deposited the gravel came from the south or south-west. The source of the river through the warping of the land, has been submerged beneath the sea, and the lower reaches raised. So much for where the gravel came from. Now the position in regard t6 the bores is somewhat peculiar. Years ago an art-esian pipe was driven in the No. 2 gardens and from this water flowed without pumping. Coming nearer to the lower, at Roope's brewei-y in Mary street a bore was put down to a considerable depth but proved useless. Another bore was put down on the Eastern Reserve but this also was a "dud. ' The next step was to put down a bore in front oi the present well, and this was a gre&t juccess. A deep bore was then put down to ever 700 feet and proved that no water existed. below the gravels we are now drawing from. It did, however, prove that Invercargill is over an ancient deep valley filled with silts and thin lignite seains, indicating an estuarine deposit. A water diviner was then called in and indicated a spot midway up the park where he said a large stream of water existed. l nis bore was an absolute failure. A concrete foundation for a pump still mar..s .ue site of this abortive attempt and stands as a monument to the fallibility of the water diviner. Two years ago a bore was put down some chains to the north of the tower and a volume of water was found. A large bore has now been sunk and the next few days will show us what results to expect. Going still farther north we find that in Gladstone water can be got easily at twenty feet. At Roope's brcwery the water rises in a well to the surfac.e a number of feet above the low tide level of the Waihopai. In the old gravel pit near the North Road the waterbearing gravel can be seen out-cropping several feet above the road, and has been proved down below the bed of the W aihopai. At Kew no water was to be had) yet at Heidelberg almost directly. behind, water is said to be abundant. At Underwood a bore again proved a failure, the strata apparently rising towardg the suface. This is not altogether surprisihg as rock outcrops at the junction of the Oreti and Makarea about a mile below and to the west of Underwwood. It should also be mentioned that bores at the Power House and on the reclamation have heen suocessful. So far as my Information goes the bores on the reclamation are considerably shallower and indicate a rising of the gtrata. The evidence of the bores is not complete, but it seems to show that the water exists in channels in very much the same way as we find the water running on

surface in the beds of wide rivers like the Rakaia. In this river, at norma! times, a number of small channels with more or less impervious banks carry the water. Only in floods does the river rise bank to bank. Channels are often filled ^nd altered. In our ancient river similar conditions may have ooeurred I will deal further with the remaining points next week.