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PUBLIC RECORD OFFICE

Reference :-

TC.O. 885

6

PUBLIC RECORD OFFICE, LONDON

ALLY WITHOUT PERMISSION OF THE BE REPRODUCED PHOTOGRAPHIC- COPYRIGHT PHOTOGRAPH-NOT TO

Its

upper

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surface is flat, and about 5 feet above high-water level, and comes out of the interior. On reaching the sea it forms a sea wall for about 40 yards, when it once more goes inland, and loses itself in the face of the bluff.

The water alongside varies from 4 to 8 fathoms.

5. The rock of which these dykes is formed (specimens 1 and 2) has generally a brownish and iron-grey external appearance, but in some of the more exposed places is white, due, no doubt, to the decomposition of its orthoclase. It is fairly hard, breaks with an uneven fracture, and in some specimens, taken from the centre, presents an amygdaloidal structure.

The weights vary considerably, and there is little or no alteration in the contiguous

rocks.

6. Along the upper edge of the above dyke are numerous cavities from 6 inches to 12 inches deep, the sides and bottoms of which are coated with a silicious deposit (specimen 13).

This specimen is of the original thickness of this deposit, and is easily detached from its bedding.

7. The sheets are also numerous, but, not so prominent, nor do they indicate clearly any one central point of emanation.

On the other hand, there appear to have been two, or perhaps three, points of emana- tion, one off the eastern, and the other off the western, end of the island, lying in a N.E. and S.W. direction, respectively, from these extremities, the former one being probably nearer to the island than the latter, seeing that the sheets are much larger on the northern face, than on the southern.

The third point was probably S.E. by E. from the eastern end of the island, and considerably further away from the island than the other two.

8. The sheet which occurs in the southern face of the western extremity has a double how-shaped appearance, the curvatures being upwards, while the string of the bow coincides fairly with the bedding of the luva.

The central part of this sheet bas, from a distance, the appearance of a dark sandstone, and is about 4 feet in the thickest part.

The rifted rock has been much altered, being generally hard and close-grained and somewhat like pitchstone in appearance.

The outer walls of the sheet are more crystalline, harder and more porphyritic (speci- mens 4, 5, and 6) than the central portions. Their exposed surfaces present a very variegated appearance, the chief colorations being red, reddish-brown, brown, grey, and pale green, this coloration being, in some cases, (especially the pale green) quite superficial, of a powdery nature, and easily rubbed off.

The whole depth of this sheet is about 12 feet in the thickest part, thinning away to nothing. There are no means of ascertaining how far it extends into the interior horizontally,

Specimen 8 is some loose sand which lay on a ledge just below this sheet, having been worn off the exposed surface of the sheet by the action of the weather.

9. The sheet which occurs in the northern face of the eastern extremity is much larger, and has, from seaward, the appearance of a large wedge-shaped mass, of yellow sandstone, the thick end of the wedge facing east, where it is about 60 feet thick.

It occurs nearer the water line than the previously mentioned sheet, its lower edge being about high water level, and extending for about 120 yards along the shore, where ft thins into nothing.

On closer examination, the central portion of the sheet (specimens 9, 10, 11, and 12) presents a very rough appearance, and entirely loses its colouring effect and shape, intruding blocks of the overlying and underlying rock making it very hard to say exactly where the boundary is.

10. This sheet is also crossed in several places by dykes, varying in breadth from 2 to 6 feet, and is penetrated by caves along its lower edge.

One of these caves is about 30 feet deep, its walls being built of the same material throughout.

Between the upper edge of the sheet and the overlying rock, in some places, are several fresh water drips, which, in wet weather, may give a fair supply of water.

The remarks made on the westerly sheet apply equally to this one, specimens 4, 5, and 6, all making their appearance, in fact the westerly sheet is to a large extent a reproduction of the tail end of this one.

11. All these sheets are penetrated irregularly by narrow reddish-brown veins of hard stone (specimen 7) which lose themselves generally in the surrounding rock.

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Along the edges of some of these veins, and then only in places, is a bright black lustrous rock, which might be Tachylite. It is flaky, and the cleavage has a polished appearance, the fracture resembling that of glass.

12. The top of the island is covered with a loose sandy soil, which has been formed from the decay of the superficial rock.

Under this soil, in some places, was found a deposit of guano, with loose stones and fragmentary ejections (specimens 14, 15, and 16).

Specimen 17 is found adhering as a deposit to several loose stones on the top of the

V. TER VEEN,

Assistant Engineer.

island.

Submitted-

E. ROOKE,

Captain.

REMARKS ON NECKER ISLAND AND SURROUNDING BANK.

Necker Island was surveyed, and the bank surrounding the island sounded out to the A plan of the 200 fathom line, between the 28th August and 10th September 1894. island drawn to a scale of 16 inches=1 mile, and a plan of the surrounding bank drawn to a scale of 1 inch=1 mile are forwarded.

Method of Survey.-A base line was measured by the angular distance of a vertical 25-foot pole (similar in construction to the 10-foot pole used in surveying) erected on the highest part of the West Peak; another pole was placed on the East Peak, which is the highest part of the island, but only 20 feet higher than West Peak.

The bearing of the base line was obtained by mean of hearings by azimuth compass at either end, the compass error being ascertained by a.m. and p.m. altitude azimuths.

The angles taken to fix the various stations are attached; when the objects were much out of the horizontal plane, a plumb line was used in taking the angle, as only sextants were available.

Method of Sounding the Bank.--Lines radiating out at intervals of two points were run in the ship from and towards the island until no bottom at 200 fathoms was obtained. The soundings were fixed at intervals by means of the compass bearing and altitude of a flagstaff on West Peak also by distances run by P. log and observation for latitude and longitude. In taking the soundings, the lower boom was got out on the weather side and topped up, an endless runner, with cut splices et 3-fathom intervals, was led through a block at the lower boom end, and another at the after-quarter boat's davit. The lead, with Massey's machine attached, was toggled to the runner and hauled out to the lower- boom, and, where the toggle was pulled out, and the lead let go by a man on the lower- boom; by this method soundings up to 36 fathoms could be obtained while steaming 4 knots. Thomson's sounding machine was also used, as well as Massey's, when off the bank. About 730 soundings were obtained from the ship.

Necker Bank was found to extend over an ares of about 400 square miles; the depths on the bank are remarkably uniform, ranging from 17 to 20 fathoms in nearly all directions, except on the south-eastern side, where a sounding of 13 fathoms was obtained with the island bearing N. 58° W., distant 20 miles; no indication of any shoaler water was seen here.

The edge of the bank is everywhere abrupt, descending from 21 to 100 fathoms in a distance of 14 miles except to the north-eastward, when the descent is more gradual.

On the bank, the bottom consists of sand and coral, on the edge, of live coral, and off the bank, in soundings of over 45 fathoms, of very fine white sand, which became finer as the water got deeper.

The edge of the bank was marked sy slightly discoloured water, tide rips, and by flocks of birds fishing.

Necker Island was found to be a bare volcanic rock, 1,380 yards long by 250 yards wide. Its southern side consists of precipitous, and, in places, overhanging, cliff, against On which the sea breaks furiously, throwing the spray for 80 feet above the sea level. the northern side is an inlet called East Cove on the plan.

Landing.-Landing may be effected here, when there is no swell, by steering in through the centre of the cove, letting go an anchor and veering the boat in to the place All gear landed has marked by a + on the plan, and jumping on to a ledge of rocks.

to be hauled up the hill, as there is no pathway. With only a moderate swell, breakers

D 3

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