Hunter. — On a Change in the Elevation of the Waikato District. 459 



Art. LIII. — Direct Evidence of a Change in the Elevation of the Waikato 

 District. By Ashley Hunter, C.E. 

 [Read before the Auckland Institute, 12th November, 1883.] 

 In December, 1875, a paper entitled " Observations on the Evidence of 

 recent Change of Elevation of the Waikato District," was read before this 

 Institute by Mr. James Stewart. In it the author endeavoured to show by 

 certain evidence that the Waikato District had at one time a considerably 

 greater elevation than it has at present. The following additional evidence 

 as bearing on the subject and going to prove most conclusively that such 

 has been the case may prove interesting : — 



In designing the present railway bridge at Hamilton it was originally 

 estimated that the cast-iron cylinders would reach a solid foundation at a 

 depth not greater than 40 feet below the present surface-bed of the river ; 

 subsequent events, however, proved that this was far from being the case. 

 The cylinders were sunk by the pneumatic process, and excavated by 

 manual labour under air-pressure until a depth of about 60 feet was reached, 

 and the air pressure of 321bs. per square inch being more than the men 

 could stand, dredging was resorted to. 



The excavation throughout the cylinder sinking showed nothing but 

 layers of pumice and quartz sand until the excavations were carried to their 

 present depths, when it was shown by the dredge bringing up large lumps 

 of hard coarse greensand that the formation of the old river-bed had been 

 struck. 



The western pair of cylinders were sunk to a depth of 80 feet, and the 

 eastern pair of cylinders to a depth of 55 feet below the present bed of the 

 river. The fact of the eastern cylinders resting upon the same forma- 

 tion as the western cylinders, but at a level 25 feet higher than the 

 latter, proved that they were resting not upon the old river-bed but upon 

 the eastern bank of the old river-bed. This is important as showing that 

 the old river must have had a very high velocity to have scoured out a 

 channel more than 25 feet deep through such a hard formation. Eeducing 

 the railway levels to high-water mark at Auckland, we find that the forma- 

 tion level of the Hamilton Bridge, which is practically the level of the sur- 

 rounding district for some miles, is 126 feet above high-water at Auckland, 

 while the level of the old bed of the river is 51 feet below high-water at the 

 same place. If we assume that in olden times the general inclination of 

 the river from this point towards the sea was the same as now, viz., about 

 9 inches to the mile, then the minimum change of elevation which we can 

 certainly assign to this portion of the Waikato District at least is about 80 

 feet. 



