Art. LXXXVIII.—Sketch of the Geology of the northern portion of the Hawke Bay. By S. Percy Smith.
Plates XXII., XXIII.
[Read before the Auckland Institute, 27th November, 1876.]
The following notes have reference to the country lying to the northwards of the town of Napier, extending along the coast of Hawke Bay to the Mahia Peninsula, and inland for a distance of from 15 to 25 miles, as is shown upon the accompanying map.
The geology of this part of the North Island is tolerably simple. It forms part of a large elongated basin occupied by rocks of the tertiary age, called by Dr. Hochstetter the "Hawke Bay series," but now I believe included in the Ahuriri formation of Captain Hutton,[1] and includes also rocks of an older date, all of which have been deposited on the flanks of the slate mountains found a few miles further inland. The greater part of the eastern edge of this basin has been gradually eaten away and removed by the action of the sea, but in the northern part of the district the westerly dip of the beds shows that part of the ancient margin is here preserved. This may also be seen a little further south, near Cape Kidnappers, where the strata all dip towards and under the Ahuriri Plains. A line drawn from near Napier in a north-easterly direction to the falls at Te Reinga on the Wairoa Biver, will very nearly coincide with the synclinal axis of the basin, towards which the strata on either side regularly dip, Scinde Island being part of the youngest formation present.
I very much regret that owing to want of time I was unable to carry my sections a few miles further westwards, so as to show the relation between the rocks here described and the old slate rocks forming the axis of the island, and which extend uninterruptedly from Wellington to the East Cape, forming the Tararua, Ruahine, and Urewera mountains. To anyone accustomed to the shapes presented by mountains of this class of rock, however, there is no mistaking their appearance as seen even from a distance of several miles. Their positions therefore will be indicated on the accompanying sections with tolerable accuracy.
That an extensive series of stratified argillaceous and sandstone rocks exists between the lowest beds shown on Section No. 1, Plate XXIII., and the slate ranges at Huiarau is evident from the appearance of the country looking westward from the high mountains surrounding Lake Waikaremoana, where every here and there the white surface of the rock has been exposed on the hill sides by land slips.
- ↑ See introduction to "Catalogue of Tertiary Mollusca," Wellington, 1873.
