2§1 



Water 32-2 



Fixed carbon . . . . . .34-2 



Hydro-carbon . . . . . . 17'0 



Ash 16-6 



100 0— J. Hectok.] 



Art. XLV. — On the Artesian Wells near Napier. 



By Captain F. W. Hutton, F.G.S. 



(AVith Illustration.) 



[Read before the Auckland Institute, September 12, 1870.] 



In" July, 1867, during a short visit to Napier, I paid particular attention to 



the Artesian wells which, just then, were being sunk on the Meanee Flats, 



and I think that a few remarks on their origin may be found useful. 



The hills south of ISTapier are composed of limestone and sandstone, under- 

 laid by a stratum of blue shale, of late tertiary age, the whole resting upon 

 clay slates, sandstones, and jasperoid slates, of a much older date. These 

 tertiaiy rocks have been denuded away towards the sea, leaving, as an outlier, 

 Scinde Island, at the foot of which the town of Napier is situated. The hollow 

 thus left between Napier and the hills has been filled up with river alluvial 

 deposits, which now form the Meanee Flats, and it is on these flats that the 

 Artesian wells have been sunk. These deposits consist of alluvial sands lying 

 upon a bed of blue clay, in which trunks of trees (matai, totara, etc.) are 

 found, and below the clay is a layer of gravel or shingle. When the wells 

 have been sunk through the first two deposits, and penetrate into the gravel, 

 the water rises in the bore-hole, sometimes to a height of twenty-six feet above 

 the surface. 



The origin of the wells is as follows : — The rain falling on the porous 

 limestone and sandstone hills, soaks through them vmtil it is arrested in its 

 downward progress by the impervious stratum of shale ; it then runs into the 

 lowest shingle bed of the alluvial deposits, which it fills. The water being 

 prevented from rising to the surface by the bed of blue clay, has no means of 

 escaping, and when the shingle bed is filled, it rises in the hills until they are 

 saturated up to the point (x) where the blue clay bed rests upon the sand 

 stone and limestone ; it then runs over in springs. When, therefore, the blue 

 clay bed is pierced by a well, the water in the shingle bed is forced up by 

 the hydrostatic pressure of the water in the hills, and overflows at the surface, 

 or rises above it, according to the amount of the pressure ; but in no case can 

 it rise above the level of the junction of the upper surface of the blue clay 

 with the limestone, or the line (x y) in the section. 



It is therefore apparent that unless the clay is pierced no Artesian well 

 will be found, and that when the boring reaches the slate rocks without getting 

 water, it may be abandoned as useless. 



