C—lo

20

range of the Kaimanawas, between Kaimanawa Creek and the east branch of the Rangitikei, much pumice still remains, more especially on those parts where the top of the range is flat and of some breadth. From the steeper slopes of this range, whether to the east or the west, the pumice has been carried into the low grounds by the action of water alone, or accompanying the material resulting from the denudation of the older rock and the formation of the deep gorges and gullies that cut into both sides of this range. As on the plains, so on this range the material gets coarser as the range is followed to the northward, and the fragments of fluidal rhyolite increase in size also. Abreast of the southern spurs of Makorako, 5,700 ft., the highest peak of the Kaimanawa Mountains, blocks of pumice up to a foot in diameter are found. Thi3 coarser pumice is for the most part seen in the saddles between the different peaks of the range, pumice being absent from the wind-swept peak itself. In positions more favourable for its retention, as on the plateau immediately north of Kaimanawa Hut, the pumice forms a covering up to 10 ft. in thickness ; and here there is a good deal of carbonised timber mixed with the pumice and rhyolite fragments, and it is clear that the old surface was covered with trees, mostly of small size, which were buried under the pumice as it fell. A study of the pumice-deposits on the plateau-tops of this mountain-range clearly shows that these accumulated in the same manner as, and as exemplified by, the deposits resulting from the eruption of Tarawera in 1886, the only difference being that in this case the material was mainly pumice. The gradual increase in the size of the fragments as the deposit is followed in a northerly direction in the Mangamaire and in the Ngaruroro Valleys indicates some point on or near the water-parting between these rivers and the streams draining to Lake Taupo as being the centre from which, by explosive violence, perhaps supplemented by the strength and direction of the wind, the pumiceous material was scattered wide over the district to the south, east, and north-east. The rapid increase in the size of the pumice fragments led to the assumption that one or perhaps a number of explosive centres would be found on the eastern side of the main water-parting, and the occurrence of rhyolite tuffs in the gravels of both the Ngaruroro and the Mangamaire, such tuffs not being found in the high-level pumice-deposits, seemed to confirm the assumption. I did not reach to the very sources of either the Mangamaire or the Ngaruroro, but the probability is that both the Ngaruroro and the Mohaka reach through the slate and sandstone mountains, and take their rise from the volcanic region to the east of Lake Taupo. In the Ngaruroro Valley I collected samples of grey rhyolitic tuff, which also occurs in the gravels of the Mangamaire. This rock, not present in the pumice-deposits, had evidently its origin near the source of the river, but in that direction, as far as sight could determine, the mountains clearly were formed of slate; but from the head shepherd on the run I learned that near the source of the "river a creek coming from the west cut through a peculiar formation answering to the description 1 had given him of the rhyolite tuffs both in the Taupo district and the Coromandel Peninsula. Not being myself able to reach the locality, he has, since my return, forwarded samples of the rocks from this west branch source of the Mangamaire, and from the description accompanying these it appears that the area of volcanic country is not great; but there is no doubt as to the existence of a volcanic deposit different from the dispersed pumice covering the mountain-tops. The area of deposit is but a few acres, and this seems to form an outlier from the great development of similar rocks within the Hinemaia watershed lying to the north. In another report * I have noted the gradual increase in the size of the pumice boulders as the Hinemaia River is followed in the direction of its source, and the same remarks apply to the other pumice-carrying rivers that fall into Lake Taupo and come from the eastward. The Rangitikei and the rivers of Hawke's Bay that, carrying pumice to the eastern sea-board, have their sources in the range of the northern Kaimanawas show also an increase in the size of the pumice fragments as their beds are followed towards the sources of these rivers. These facts lead to the inevitable conclusion that the pumice had originated in the region to the north and north-west. It is, however marvellous, at least conceivable that, blown to a great height, the pumice drifted to the south-east and north-east, and was deposited as a covering more or less thick over the area described, and over a yet more extensive area within which such air-borne pumice is now obscured or has been washed away. Within the watersheds of the Rangitikei and the Ngaruroro it is evident that a heavy deposit of pumice was deposited as material borne through the air from eruptive centres on the northern borders of the district. This deposit accumulated rapidly, and was perhaps the result of a single eruption. Such light and loose material did not long remain on the steep slopes of a mountain region, and along all the valleys of the district terraces remain that indicate the height to which they were filled by the rapid translation of the pumice from the mountain-sides to the lower grounds. In the upper valleys of the Ngaruroro, Taruarau, and Mangamaire pumice suddenly accumulated to depths varying from 100 ft. to 120 ft., or more, through which the streams have again cut channels to the bed-rock, but leaving fringing terraces still indicating the height to which their valleys were filled. These terraces are formed exclusively of pumice, there being no slate or sandstone fragments present; and, what is perhaps more remarkable, the rhyolite associated with the pumice of the mountain-tops is not represented. This shows that the accumulation of the pumice was not a gradual process during which the lesser gullies in the older rocks were deepened, as otherwise, in spite of the difference in specific gravity of the material, heavier material would have been carried forward, and been mixed with or formed beds between the different thick beds of pumice. The gravels of these rivers do not at the present time show much pumice, pumice washed out of the terraces or off the mountains being carried away to beyond the mountain region; and this is another proof of the vast quantity and suddenness of the pumice-deposit that could have filled these mountain-valleys to a depth of 120 ft.

* Mines Reports, 1899, 0.-9, pp. 16-31.