AN INLAND SEA.

Marlborough Express, Volume XLII, Issue 216, 11 September 1908, Page 3

AN INLAND SEA.

IN THE NORTH ISLAND

The report on the Tongariro Na-' tional Park recently presented to Parliament contains a very interesting section, contributed by Mr R; Speight, F.G.S. Discussing the geological history of the district, Mr Speight sates that the oldest rocks in tlie neighbourhood of the park are the slates and sandstones of the Kaimanawa Mountains. These are probably of carboniferous age, and form a portion of the structural axis of older rocks which extends through the North Island from near Wellington towards the eastern side of the Bay of Plenty. The southern portion of the Kaimanawas, at any rate, is part of a plain of marine denudation formed in tertiary times, and the tolerably level surface then acquired was subsequently raised above sea-level and thoroughly dissected by stream-action, so that now" it is composed of a number of more or less isolated elevations. At the time of the submergence a great bay or strait must have occupied the middle of the North Island, extending north-east from Wanganui and probably cutting off the submer- 1 ged parts of the Kaimarawas and Ruahines from islands lying to the north-west. An achipelago then occupied the area now covered by the North Island. Thick and extensive deposits of marine clays and limestones stretching in a broad band from the Ruahines across the middle courses of the Rangitikei, Wangaehu, and Wanganui Rivers towards the Tasman Sea in the west, prove that in miocene times the sea transgressed over a great area in the south-western part of the island. No doubt, says Mr Speight, a line of weakness in the earth's crust extends in an approximately straight line from Ruapehu through Tonga and Samoa towards distant Hawaii; This line may perhaps be called the "Maori line" of volcanoes, as no doubt the first Maori immigrants to the country followed its direction more or less closely, and the legends of the native race contain references which show clearly that they recognised the linear arrangements of the vents and their common origin. Activity is more pronounced now at the northern end of this line, perhaps owing to the fact that another earthfissure crosses it, running wost-north-west and east-south-east—i.e., approximately at right angles to the Maori Jine. The great volcano of Savaii, in Samoa, is placed at their intersection, and hence its continuous activity for the past few years. The Hawaiian line is parallel to, %he Samoan line, and the Maori line when prolonged intersects it at the centre of its greatest activity.. There are thus two intersecting sets of telluric cracks crossing the Pacific Ocean. It is likely, thinks Mr Speight, that Ruapehu will be active again—perhaps not in the near future, but almost certainly after a long space of time. Its general form, the character of its lavas, though not in themselves absolutely sufficient to warrant the prediction as certain, yet suggest that Ruapehu has not passed through all the phases of its life-history.