H.—l7

4

recourse to in order to overcome this difficulty. At Dilman's Town, Kumara, where there are 340 acres of proved payable auriferous ground in one basin —■ being two miles of the ancient bed of the Teremakau —advantage has been taken of the lower level of the present channel of that river, by running tunnels from it through the intervening terrace formation to a level below the auriferous deposits. Through these tunnels the sludge flows in a rapid current from the claims, and is shot into the deep bed of the Teremakau. There are several private tunnels in operation, and the Government has a tunnel sludge-channel of 87 chains in length in course of construction, the lower half of which has been completed and timbered in a very substantial manner, and it can be availed of as soon as the claim-holders have made their branch tunnels into it. The section of this tunnel is 11' by T It may be compared, as in reality it is, to a gigantic underground sewer It will cost over £14,000. The open sludge-channel at Naseby is another large public work of this class, it is 8 miles long, and cost £23,492, The conditions, however, for disposal of tailings are rarely so favourable as at Kumara and Naseby, especially at the former, and sludge-channels become impracticable where there is little fall. Recourse must then be had to the more expensive and laborious process of tracing the auriferous ground by tunnels, and raising it up a shaft to a platform sufficiently high to allow of fall for the tailings after the stuff is washed. This plan is adopted with great success at Orwell Creek, Ahaura. But the most ingenious expedient for overcoming the tailings difficulty is in operation at Gabriel's Gully, Tuapeka. In that gully there is an accumulation of millions of tons of tailings from the earlier workings of the famous Blue Spur This mass of stuff, and portions of the original ground on which it rests, have long been supposed to be payable if they could only be put through the sluice-boxes in a wholesale manner There is plenty of water available, but not sufficient fall. The problem seemed insoluble until Mr J R. Perry took it up. By his plan the stuff is forced up a pipe by a powerful jet of water let in from a nozzle at the lower end of the pipe. This jet has a head of over 300 feet, and so great is the suction induced by its ascent that as the stuff is fed into the lower end of the pipe by a stream of water it is at once drawn in and rushes up the pipe, and would be discharged at the top as from a catapult or volcano but for an iron hood which serves the double purpose of breaking any agglomerated nodules, and guiding the stuff within the sluice-boxes, along which it is carried by the water, and is shot over at a convenient distance from the workings. In this way the stuff, instead of being washed bodily away down a sludge-channel, is simply turned over and shifted a feAV hundred feet at most. By referring to Mr Carew's report in the Appendix a more detailed description of this ingenious plan will be found. It is a great mechanical success, and will pay, it is estimated, if the ground will only yield a few grains of gold per ton. As another instance of the skill and enterprise at work in the development of the alluvial deposits, the dredging of the bed of the Clutha may be cited. Eor many years dredging-machines have been at work on that river The principle and system of raising the stuff by a chain of buckets in these machines are almost identical with that of harbour dredges. They are moored on the river, the powerful current of which acting on paddle-wheels supplies the motive power which drives the buckets. The bed of the river being very rich at places the dredging has proved profitable to many But the dredger, depending on the current of the river for power, can only work where that is strong. Another plan was to have a punt or platform moored on the river, and by means of a large scoop with a strong canvass bag attached stuff was raised by a lever, this was a very laborious process. Another plan was on the pneumatic-tube principle employed in sinking cylinders for the piers of bridges. In it, the miner was let down and worked on the bed of the river direct. But there was too much time and expense involved in shifting the tube, and this plan was soon abandoned. There was also a plan of submarine boat on the principle of the diving-bell, the boat and apparatus were constructed, but the project fell through. The dredger principle is the one approved by experience, and there are now four steam-dredgers to be placed on the river They, of course, will be independent of current, and