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the opening. Sometimes the opening is completely closed, and drainage is effected by percolation through the bank. Spits frequently tie islands to the mainland. Excellent examples of this can be seen at Ocean Beach, near Dunedin ; at Lyall Bay, near Wellington ; and far north of Auckland, where the ancient mountain-headlands lying between Cape Maria van Diemen and the North Cape are joined to the solid land near Mangonui by the best-developed sandspit and sand-dunes occurring in the Dominion. (ii.) Material of Dunes. The material out of which dunes are built consists for the most part of small particles of the more resistent constituents of the rocks of the land surface. Quartz-grains usually form 90 per cent, of the whole. This is due to two main causes. (1.) Quartz is a very widely distributed mineral in rocks of the earth's crust. ft forms the greater part of all sandstones, and is an important constituent of many other rocks. (2.) It is a mineral not susceptible to the action of weathering-agents ; it resists the action of all acids occurring naturally, and it is extremely hard. Owing to this cause its importance is always increasing as a constituent in the Waste of the land ; other minerals surfer decomposition, or are worn away, but quartz survives, and so its percentage becomes greater as tic products of erosion are subjected to further disintegration and weathering. Other minerals play an important though subordinate part in the formal ion ol dunes viz.. feldspar, iron-oxides, hornblende, augite. and limestone, and with these occur occasionally thi minerals, zircon, rutile. and tourmaline. Their power of resisting decomposing-agents explains their presence also. But account must be taken of the character of the rock which has furnished tin' material of dunes when speaking of the mineralogical character of the individual grains. A sandstone or quartz rock produces sand consisting almost wholly of quartz-grains. As the main mountain-ranges of the North Island and of the eastern part of the South Island are composed principally of sandstones, greywackes, and slates, the sands on the eastern shores of the South Island and of the south of the North Island contain a high percentage of quartz. Slate:, weather into very fine particles, and usually form mud. Granites, gneisses, and schists produce a sand with predominating quartz-grains, unless bhe parent rock is of basic type. Feldspar and mica are of subordinate importance, for the reason that. although they may be predominant in the solid rock, they are less able to resist attrition and decomposing-agents. Mica is a very important constituent of river-sand, but ii becomes rapidly shredded out into thin films, and is finally carried away when exposed to wind action in a. dune. Sands of this type occur on the beach at St. Clair, derived in all probability from the Central Otago schists by the agency of the Clutha and Taieri Rivers, and carried north by the strong shore current running up the coast. The sands from volcanic rocks depend in composition on that of the parent rock. Pumiceous and scoriaceous varieties are extremely common in the North Island, and the titaniferou of the west coast are largely derived from the breaking-down of the volcanic rocks of Mount Egmont and of the Central Plateau. Little or none of this sand, is found farther east in Cook Strait than the mouth of the Rangitikei River. That on the shore between there and Porirua owes its origin to the disintegration of the quartziferous rocks of the Ruahino and Tararua Mountains, and magnetite is absent. One point should be noted here. The black sand of the Taranaki coast contains a good deal of hornblende and augite grains, both dark in colour, but of no value as a source of iron. These minerals have also been weathered out of the volcanic rocks, and at first sight are indistinguishable from the magnetic ironsand. but they detract very much from its value as an ore. and will have to be separated before it is treated metallurgically. Similar magnetic sands occur in smaller quantities on other stretches of coast. Small patches of fairly pure titaniferous magnetite are to be found on some of the beaches of Banks Peninsula. di rived from its basic volcanic rocks : and also on the west coast of the South Island, weathered out met amorphic rocks and basic volcanics of Westhind. It is stated by P. G. Morgan (122. p. 110). " The beach-sands of West land consist mainly of quartz. Magnetite is a noticeable constituent, whilst garnet and zircon are fairly common, the former being especially abundant on bhe bead ar Ross. More or less fine gold is always associated with the ilte." This mineral forms an important constituent of these sands because of its hardness, iis resistance to chemical decomposition, and its tendency, owing to its weight, to accumulate in es by the ordinary process of water concentration. A cursory examination of specimens of New Zealand dune-sands shows that they are largely composed of quartz, with subordint . hornblende and augite, and feldspar, in that order of importance ; but subsequent examination may lead to a modification of this statement. Limestone formed from shell-fragments is very common in some places, and at tine he main bulk of the sand. Its presence is a. distinct advantage, as ii forms a valuable cementing-agent, and thus lends to fix the position of dunes. (iii.) Form ok the Sand-grains. The sand-grains of dunes exhibit certain peculiarities of form which distinguish them from ordinary river and sea sands. The latter are angular or subangular in shape, as they have not been subjected to the abrasion winch dune grains have to endure. Although stones and gravel are invari ably rounded by the continual friction as they are roiled along by river or sea. the smaller particles re or less protected by an enveloping film of water, which, as they become smaller, prevents that close contact necessary for rapid abrasion. However, the corners and edges oi the grains get worn off in process of time But when sand accumulates as dunes, and there is no protecting envelope