The weakness of these forts as regards standing a siege was that in none of them did there seem to have been wells sunk or any provision made for storing water in large quantities. And although always built near a stream, the besieged would be obliged every now and then to elude the vigilance of their enemies at night-time and renew their supplies of water by fetching it up to the fort from the stream below. But otherwise these forts were provisioned with quantities of fern roots and dried fish. The people's only weapons seemed to be lances, pikes, and halberds of wood, pointed sometimes with jade[77] or bone, and heavy jade clubs and axes; but they had no bows and arrows or slings, and very few weapons that they could throw. [77] Jade, which is so often referred to (though sometimes miscalled "green talc") in the works of early Pacific explorers, is a beautiful green stone of several quite distinct species. The Jade of New Zealand is either a fibrous silicate called nephrite or a green serpentine silicate. The Maoris called these green stones _poenamu_ or _poiinamu_, and because Jade of both kinds was specially abundant in the South Island this was called Tarai-poenamu=the Land of Jade. On 20 November, 1769, Cook discovered a river at the head of a great inlet, which he named the Thames, and in this region of the North Island he noticed the splendid kauri pines.[78] One of these he judged to be 89 feet from the root to the first branch, and perhaps 200 feet high altogether. Its girth near the ground was nearly 20 feet. In the most northern part of the North Island they met with the paper-mulberry tree growing in the native plantations, and here they frequently found a kind of celery, which was eagerly gathered by the seamen as a vegetable addition to their diet. [78] See pp. 35 and 42. In December, 1769, they rounded the northernmost promontory of New Zealand, which Cook at once identified with Cape Maria Van Diemen of Tasman's discovery, and perhaps realized then for the first time that the Terra Australis along which he had been coasting was none other than the New Zealand discovered by Tasman. The natives in this northernmost part gave a very interesting description, through Tupia the interpreter (when asked if they knew of any other land besides New Zealand), and said that far away to the north-west there was a country of great extent, which they called Ulimaroa, and which had been reached by some of their people in a very large canoe after a month's sail. The most striking feature to them in this distant land was that its inhabitants possessed and ate pigs, and they called these pigs by the widespread name, _bua_. It is probable that the land to which they alluded was Fiji; for though New Caledonia answers better to the description, the people possessed no pigs when this large island was first visited by Cook.