19

o.—lo.

Range it is very thickly deposited, being often in the gullies 6 ft. to 8 ft. thick. The extensive terraces of the Lower Mohaka River (which contain as large a quantity of level land as is to be found in the district) are thickly covered with it, thereby rendering them unfit for cultivation. Towards the east the deposit gradually thins out, until approaching the vicinity of Poverty Bay very little of it is seen. The only spots that are free from it are the lower terraces of the rivers and the surface-slips ; and, as the country lying along the coast is the most subject to these slips, as mentioned above, it is here that the pumice has in a great measure disappeared, thus allowing the grasses to spread. "The general opinion appears to be that this pumice was ejected from Tongariro and the adjacent volcanoes, and was spread over the surface of the country by the wind ; and there are certain considerations which favour this view, such, for instance, as finding the greatest thickness of sand on the lee side of the high ranges, where it would naturally accumulate, and also from the fact that the size of the particles appears to diminish as we recede from the supposed centre of distribution ; but at the same time this will not account for all the facts. An examination of the sand seems to show that all the particles are water-worn or abraded, and that many of them are too large to be carried by an ordinary wind, being sometimes as large as walnuts, though the average size would be about an eighth of an inch in diameter. " The only other hypothesis which would account for the presence of the pumice over such an extent of country is that it has been carried into its present position by water. No doubt many of the extensive pumice-drifts of the North Island do owe their origin to that cause, notably the pumice plains of Kaingaroa, near Taupo, which in places are regularly stratified, and often contain trunks of trees, lying in a horizontal position, converted into charcoal. But there is a great deal of difference between the pumice-deposits of Taupo, the Waikato, and the inland portion of Taranaki and those of northern Hawke's Bay. The former invariably occupy level plains or depressions which no doubt were at one time lakes. To my mind, a deposit of a light substance like pumice, which ordinarily floats on the surface of the water, is only possible in enclosed sheets of water which would not allow of its escape. If it once reached the open sea it would be carried far and wide by the winds and currents. There is one thing, however, which should not be forgotten, and that is that the enclosed air, to which pumice owes its buoyancy, might under pressure be driven out, in which case, of course, it would become water-logged and sink, and would then form regular aqueous deposits like sand or clay. That such deposits are sometimes met with I think every one must allow who has seen the Kaingaroa Plains, or the beds of white coarse sandstone near the Miranda Redoubt, which is, I think, without doubt, formed of pumice sand, consolidated under pressure, and the deep pumice strata found in the Tauranga district. " I observe in the last volume of the Transactions of the New Zealand Institute that Mr. J. C. Crawford, of Wellington, in his paper on ' The Old Lake System of New Zealand,' has touched upon this subject, and comes to the conclusion that the great central pumice-drifts are lake deposits. In this I entirely concur, as far as relates to the country described by Mr. Crawford, but I think that the lake theory cannot be implied in this district. The large extent and great height of country over which the pumice is scattered precludes the idea that it is entirely due to the action of water, whilst the fact that the thickest deposits seem to be confined (in this district at least) to the northward of a line drawn in a due east direction from Ruapehu would add force to the argument that it was spread out by the prevailing westerly winds ; and the water-worn appearance may be explicable on the supposition that it is due either to decomposition or to the attrition of the particles as they were ejected from the volcano. The amount of evidence, however, is not sufficient to come to a conclusion either way; nor are we justified in ascribing to Tongariro and its adjacent volcanoes the origin of the whole of this pumice until a thorough exploration of the mountainous Urewera country shall have proved that it did not emanate from some nearer source." Mr. Cox was correct in stating that pumice sands occur in the marine strata of northern Hawke's Bay, and possiby correct as to the origin of a good deal of what he saw over the surface of the low grounds. Captain Hutton might have noted pumice sands elsewhere and in other beds than the superficial deposits on the Totokura Saddle, and Mr. Percy Smith overlooks the fact that part of the pumice-covered area described by him contained pumice derived from Tertiary marine beds which was necessarily to some extent " water-worn or abraded." He is quite correct in ascribing to the action of the wind the rounding of the pumice that could not have been derived from the Younger Tertiary rocks. Much larger pieces of pumice are found on the higher part of the Mungaharuru Range than fragments that might be equal to the size of a walnut. As to the position of the volcanic vents from which the pumice was ejected, none of these are located in the Urewera country outside the watershed of the Tarawera River and the eastern upper tributaries of the Rangitikei. It is possible—nay, it is highly probable—that in the mountainous region to the north-east of the Napier-Taupo Road, between Tarawera Hotel and the margin of the Kaingaroa Plain, the volcanoes of that part yielded pumice. From the volcanic region, east of Lake Taupo acid rocks extend across the Napier-Taupo Road from a point four miles west of Tarawera Hotel to the eastern edge of the Kaingaroa Plain, but if such rocks reach into the Whakatane watershed they do so only as capping the higher mountains with lava-streams and tuff-deposits. Over the Inland Patea district and the Kaimanawa Mountains also from the line of road north to and over the greater part of the Waikato watershed, superficial pumice-deposits are met with, as originally deposited. On the open plains and downs of the southern part the deposit is not thick; the material is fine, and consists almost exclusively of pumice fragments, but when followed to the north, on reaching the base of the Kaimanawa Mountains, the pumiceous material is coarser, and small fragments of fluidal and spherulitic rhyolite are found mixed with the pumice. On the outer eastern range of the Kaimanawas there is very little pumice left in place, this having gravitated into the low grounds, and been deposited along the creek- and river-valleys. On the second