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Position of the Cave.
When the cavity now called the Moa-bone Point Cave was enlarged by the waves of the sea, the estuary of the Heathcote-Avon in its present form was not yet in existence. Close to this cavity, on its western side, a hard doleritic lava stream, now passed through by the Sumner Road cutting, reached for some distance into the sea, forming a small headland, against which, principally on its eastern side, the waves of the Pacific ocean broke with considerable force. Masses of rock were detached by the surf being taken along in an easterly direction for about a quarter of a mile forming a ridge, gradually becoming lower and losing itself amongst the sands.
The formation of this ridge principally took place when this portion of the peninsula was some 12 to 15 feet lower than at present, the upper line of boulders being about 16 feet above the present high-water mark. When the land rose again the sea was cut off by this boulder ridge from the entrance of the cave, a huge rock lying here nearly across, protecting it at the same time from being filled up by the deposits of drift sands now forming on the flat close to it.
A second and lower line of boulders was formed in front of the former, about 5 feet above the present high-water mark, with a small terraced space behind it. Since then other deposits, formed in the A von-Heathcote estuary, have been added as a small belt in front of this last line of boulders, brought into its present position by the action of the open sea.
In section No. 1 (Plate I.), I have given the necessary details in illustration of these points.
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Section Near Sumner From Estuary of River Heathcote to a Cave.
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Before giving a description of the cave as I found it before beginning my labours I may observe that the same was well known from the very beginning of the Canterbury settlement. It was even inhabited by some of the earliest settlers, and for some time afterwards afforded shelter to lime-burners, fisher-men, and road parties, of whom, as will be seen in the sequel, ample traces were left behind.
The entrance of the cave, which is about forty feet from the crown of the Sumner road, which has here an altitude of 18.59 feet above high-water mark, is situated nearly 5 feet lower, or 13.64 feet above high water, taking the level of the surface for our line.
An opening, which is about 30 feet broad by 8 feet high, being, however, much narrowed by a huge rock, leads into the cave, of which I found the floor slightly sloping down. The cave itself consists of three compartments, of which the first one possesses by far the greatest dimensions, running nearly due north and south, and being 102 feet long, 72 feet broad towards the middle, and about 24 feet high.
From its termination, by a small passage a second cave is reached, which is 18 feet long, 14 feet wide, and about 11 feet high; its direction being north by west to south by east; at its southern end a small passage, 3 feet high, by about 2.50 feet broad, leads into a third or inner chamber, which is 22 feet long, with an average width of 16 feet, and about 20 feet high, running again like the principal cave due north and south; its floor being about eight feet above high-water mark.
My best thanks are due to Mr. T. Roberts, the present engineer of the Gladstone and Timaru Board of Works, who, at my request, has taken the necessary levels and surveyed the cave, the result of his labours being attached to this report.