Page:Transactions NZ Institute Volume 9.djvu/620

Rh all the particles are waterworn 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 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 the 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 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 coarse white sandstone found near the Miranda Redoubt, which is, I think, without doubt, formed of coarse 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 applied in this district. The large extent, and great height of the 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 deposit seems to be confined (in this district at least), to the northward of a line drawn in a true 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