292 Transactions. — Geoloijy. 



not less than 600 millions of tons, must cause a slight compres- 

 sion of the beds, and this would tend to keep back the fresh 

 water from entering the ocean as freely as under a diminished 

 pressure. This would result in a temporary accumulation in 

 the direction of the point of outflow, which, with the increased 

 pressure, would probably cause a higher flow to take place from 

 the wells. A similar effect might be expected upon the artesian 

 wells by the percolation of river water into the overlying beds 

 on the plain, especially during times of flood. I believe that 

 this increase in the artesian flow has been noticed about 

 Hastings at the time of flooded rivers ; and the natural inference 

 has been that the artesian supply comes directly from the rivers 

 Ngaruroro, Tukituki, and Tutaekuri by percolation through the 

 shingle, as the rivers wend their way across the plain. 



As for the origin of the water-supply, little can be stated 

 with certainty. We know, however, that it cannot be by soakage 

 through overlying beds, the one immediately overlying the shingle 

 in which the water is found being impervious equally with the 

 one underlying it. From this it follows that the rainfall on the 

 Heretaunga Plain proper cannot affect the supply in any way 

 whatever. It seems to me that the large quantity of water that 

 is constantly passing underneath the plain, is to be accounted 

 for by the presence of numerous under-ground springs at the 

 junction of the limestones and the clays which underlie them, 

 and by the percolation of river water through the shingle and 

 sands at the outcrop of the beds. All the hills surrounding the 

 district under notice are made up mostly of limestones, sands, 

 clay, pumice sands, and shingle ; and the same may be said of 

 the rocks to the westward, even as far back as the eastern flanks 

 of the Kuahine Mountain Range. All these rocks are exceedingly 

 porous, and water passes through them most readily. 



The limestones about Havelock, and the shingle conglome- 

 rates, clays, and pumice-sands at the Kidnappers, dip directly 

 underneath the plain. So do the conglomerates and pumice- 

 sands at Redcliffe, and so do the shingle and pumice deposits 

 to the north-west of Maraekakaho ; and we may expect to find 

 large and important underground springs at the junction of 

 these bods and the underlying clays. During my recent visit to 

 the volcanic district of this island, one of the most remarkable 

 sights, among the many remarkable ones to be seen, was the 

 source of the Tokaanu River, which rises not a mile and a half 

 from the southern shore of Lake Taupo, into which lake the 

 said river discharges itself. At the base of one of the spurs of 

 the now dormant volcano, Pihunga, a spring bursts from the 

 ground, just after the manner of an artesian well, and the 

 volume of water is so large that a river of no small size is at 

 once formed as if by magic. The whole country around, both 

 mountain and plain, is made up of porous rocks, and rain 



