438 Transactions. — Geology. 



is much wider than the level way under formation. This process 

 in a large measure illustrates the growth of the Heretaunga 

 Plain. The material that the rivers brought down spread out 

 fanlike in different directions, and. as the area of deposition 

 filled up, the river was extended seaward, and it may be that 

 the direction of deposition was altered or modified. This is 

 plainly seen in the case of the Rivers Ngaruroro, Tutaekuri, and 

 Tukituki, which have frequently altered their course, so that the 

 fanlike deposits have spread themselves in large measure over 

 the whole of what was a sunken area that extends from the 

 fractured limestones at the back of Havelock to the limestones 

 between Crissoge and Roy's Hill — that is, from north-west to 

 south-east. 



It is the deposition of the material from the rivers that has 

 produced the bedding from which the artesian-water supplies 

 are now obtained, and the varying character of the material 

 brought down will help to explain why the whole of the beds 

 underneath the surface are made up of similar deposits. Recog- 

 nising, then, that as the filling- up process went on the sea was 

 thrown further back by the making of the land, there will be 

 little difficulty in understanding how at the present time the plain 

 of which the occupied part is known as the Heretaunga Plain 

 is a good deal larger than that which is at present above the 

 level of the sea. 



For purpose of reference, let the place locally known as the 

 Washout, near Waitangi, be taken as the starting-point, and 

 let us suppose that a place out in the bay is selected, fourteen 

 miles away, and eight miles to the north-west of the Kidnappers. 

 This area is almost a counterpart of the Heretaunga Plain. 



The depth of the sea fourteen miles from the Washout in the 

 direction of Mahia Peninsula is 168 ft. At twelve miles the 

 depth is 144 ft., at ten miles it is 108 ft., at eight miles it is 90 ft.. 

 a1 six miles 72 ft., at four miles 60ft., at two miles 48 ft., and 

 at one mile the depth is 24 ft. Suppose there was no water over 

 this portion of the bay, the land would he as Hat and the slope 

 as gradual as the Heretaunga Plain itself between Roy's Hill 

 and Waitangi. This plain was formed in its greater part under 

 similar conditions to the Heretaunga Plain, and, geologicallv 

 considered, is contemporaneous with it, and forms a portion of it. 

 The shingle beach that is so characteristic of the coast between 

 the Kidnappers and Petane forms no portion of the plain under 

 notice. Its history is limited to the time when the Tukituki 

 broke through the limestones at the gorge near Te Mata, and 

 subsequent to the final separation of Scinde Island from the 

 mainland in the direction of the Quarantine Station. The 

 shingle along the beach is limited both in breadth and depth. 



