GooDALL. — Water Sup'jily for Auckland. 3 7 



obtained from Mount Eden, it will be necessary to prove the depth of the 

 basin or floor of the volcano, its shape, height of the rim of the basin at its 

 lowest part, probable direction of the flow of water from it, summer level 

 (minimum) of water, and inclination of the water from the rim of the basin to 

 its outlet at the springs. 



. A part of these questions may be answered by a survey of the ground, and 

 by obtaining levels — that is, by surface examination ; and the entire question 

 would be solved by adding to the above a series of bores. A survey of the 

 ground would determine the probable shape of the rim of the basin, also the 

 course of the water travelling beyond the rim. The lava streams having run 

 in the old valleys formed by the tertiary rocks, indications may yet be obtained 

 of the course of the bottom of that valley by the run of the lava and other 

 indications, such as the outcropping tertiary formation ; and, as the overlaying 

 lava rocks are of a very porous nature and abounding in large cracks and 

 cavities, any water pouring from the hills above (after rain) would undoubtedly 

 flow through the ancient valley, but would occupy more space, have a greater 

 inclination, and would take more time to flow than were it unimpeded. 



Having completed the survey, it will then be advisable to put down a 

 series of bores between the site of the reservoir at Gilfillan's corner and Mount 

 Eden. These bores, put down between the limit of the scoria and half way to 

 the centre of the hill, would probably be sufficient to give the depth and shape 

 of the basin. This will be important to ascertain accurately, as on that side 

 the necessary shaft would be sunk, and a correct knowledge alone could be a 

 guide as to the depth of shaft and distance of a drive to tap the water. Then, 

 at a point to the westward of the hill facing the lava flow, another series of 

 bores should be started, beginning at about half-way down the hill, over the 

 rim of the basin, and thence along the probable course of the subterranean 

 stream to its outlet at the springs. These bores would determine the depth of 

 the basin, the permanent level of water, and the inclination of the water 

 towards the springs. Having all these data, it can now be calculated, without 

 much trouble, what available water there is ; and by the height of the i-im of 

 the ba.sin may be determined how much extra supply can be obtained from 

 the outward flowing stream ; for the lower the rim is, the better will it be, as 

 then, by pumping at Mount Eden, any insufficiency of water in the basin 

 would be supplied by infiltration. Having arrived at this stage, it can be 

 positively ascertained if there be an adequate supply or not ; and, if there be, 

 a shaft will have to be sunk, and pumping machinery erected for supplying 

 the reservoir. 



There are two available sites for a shaft, one being at the proposed 

 reservoir. If this be fixed upon, the shaft should be sunk to the level of the 

 bottom of the basin under Mount Eden, unless that exceeds high-water mark, 



