288 Transactions. — Qeology. 



the limestones, marls, shingle, and pumice sands at Te Mata, 

 and subsequent to the separation of Scinde Island from the main- 

 land in the direction of the Quarantine Station. The shingle 

 spit is limited both in breadth and depth, and began to be formed 

 when a large portion of the present plain was above water level. 

 It is not more than from 60 to 70 feet in depth, and its average 

 breadth I estimate at less than 400 yards. If this beach were 

 taken away, just as we have supposed the water in that portion 

 of the bay between Napier and the Kidnappers to be taken 

 away, there would be seen a valley plain, 30 miles long and 

 •rom 8 to 10 miles broad, so flat, and so gradual in its slope, 

 that the most perfect eye could not distinguish the inclination of 

 the beds. I have pointed out that a mile or so to the west of 

 Koy's Hill the plain is 166*4 feet above sea-level ; whilst 15 

 miles out in the bay, or 30 miles from Roy's Hill, the sea is 

 only 174 feet deep, or a difference of 340*4 feet between the 

 highest and lowest points, with a gradual slope the whole way. 

 This gives a fall of only ll£ feet to the mile, or little more than 

 a foot in each 480 feet of horizontally. Now these, to me very 

 interesting facts, are of great importance in helping us to arrive 

 at a proper conception with respect to the artesian water supply 

 on the plain. Two or three miles outside the 15-mile limit in 

 the bay the ocean bed is composed of blue clay. This clay is 

 the underlying impervious bed which passes under the plain 

 throughout its full extent. The same bed is met with about 2.1 

 miles beyond Maraekakaho, where it is seen coming to the sur- 

 face in the Maraekakaho Creek. At one time the sea washed 

 over the whole length of this clay bed ; but the sea has been 

 slowly receding, in consequence of the debris brought down by 

 rivers from the west, and deposited in what was once an arm of 

 the present bay. All the beds which overlie this impervious 

 clay-bed have been deposited in a constantly diminishing, or 

 rather in a constantly-varying, thickness, as they get further and 

 further from the source of supply, which, at the beginning of the 

 plain formation, was the mouth of a large river then situated at 

 Maraekakaho. It needs no explanation on my part to account 

 for the constant thinning out of beds as they proceed from 

 Maraekakaho outwards. Any observer can see the same thing 

 happening daily, wherever water is removing debris and re- 

 depositing it under conditions where the movement is free. As 

 remarked above, the lowest impervious bed is a blue clay of a 

 somewhat irregular surface, having a north-east inclination, and 

 troughed along its north-west and south-east edges. On this 

 clay is to be found an overlying series of irregular beds composed 

 of shingle, sand, impervious blue clays, blue sand, shingle, 

 pumice, lignite, pumice and clays, shingle, pumice, fine mud, and 

 sediment, in ascending order. All these have been brought 

 down bv the rivers and creeks which have at different times 



