570 ■ , Transactions. — Geology. 



filled up by the process of denudation from the hills, and by 

 means of the material which the rivers have brought down in 

 the wet season. An imaginary line from the top of the Kaiti 

 Hill to the hills behind the Hon. Mr. Carroll's homestead, on 

 the Whautaupoko, thence across the lower Patutahi Hills, 

 near Mr. Sutherland's, and onward to the hills up the Ormond 

 Valley, joins together all the porous beds which at one time 

 covered the whole of the intervening area. 



It will be noticed how great the changes in the land features 

 have been since these contemporary deposits took place. I 

 am in doubt whether the whole of the enclosed area forming 

 the plain is one of denudation and deposition or of depression 

 and deposition. It may be there is a combination of the two, 

 as there is evidence in support of each. The sinkings for 

 artesian water that were carried out in several spots within 

 the Gisborne Borough some years ago show a denuded surface 

 only, but the wells at Matawhero and Makauri imply an area 

 of depression, followed by one of deposition, from the material 

 which the Waipaoa Kiver has brought down and deposited over 

 a deltoid area. 



If the plain was the outcome of denudation only there would 

 be little hope of finding an artesian-water supply, and even as 

 an area of depression the enclosed basin may be expected to 

 be of small extent, and special care is needed in the selection 

 of a suitable place for putting down a trial bore. I have 

 pointed out that the Waipaoa Eiver passes across the trough 

 of the porous beds which are to be found in different places 

 within tlie boundaries of the district. These beds are absent, 

 except the upper very recent ones, within the limits of the 

 Gisborne Borough, and this is the reason why water was not 

 met with in the trial bores that have been put down. The 

 beds that dip under the town are those belonging to the Kaiti 

 beach series, and they are mainly made up of clay, and are im- 

 pervious to water ; besides, the outcrop of the beds cannot pos- 

 sibly have more than a tithe of the quantity of water needed 

 for the supply of the town, as the area of drainage of the out- 

 crop beds is too limited in extent. It is quite useless tO' 

 attempt sinking for an artesian supply within the limits of the 

 borough — at least, I could not recommend any one to do so, 

 because the money would be wasted, as there is no real 

 artesian basin in the immediate vicinity of the town. But 

 within certain limits the prospects of obtaining an artesian 

 supply are good, the limits being within what appears to me 

 as the area of depression to which reference was made above. 

 This area is not of great extent, but it is sufficiently large to 

 allow of a fair number of wells being put down should the 

 water be suitable for domestic purposes. The line of de- 

 pression extends in a line from Ormond to the most easterly 



