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more equal distribution of the weights and pressure in sections 3 and 4; as it would most probably admit of weight being removed from the one where there is at present an excess, to that where pressure preponderates,—and, in fact, to a much more equal distribution throughout the whole body.
The following alterations would also contribute to a better distribution than the present.
Let the bower and sheet cables be stowed further aft; the stream cable and hawsers abaft them, in the space now occupied by cabins, slop-room, &c.; and the stores, at present stowed in the foremost section No. 5, removed aft to the fore part of the cable tiers; a part of the bread, slops, beds, marine clothing, &c., as in the former proposal, to occupy the present place of the sea-stores in section No. 5. By such arrangements the weight of the stream cable and hawsers, and part of the bower cables, would be removed to section No. 2; the sea-stores to No. 4; and the weights reduced at both extremities.
The excess of weight would not only be considerably reduced in the fore extremity, by the proposed alterations ; but at sea, if desirable to lighten this part as speedily as possible, a regular decrease, in a 74-gun ship, of two tons per week, may be calculated on, till the expiration of half the cruise, when the fore bread-room would be cleared.
By a minute inspection and measurement of the different parts, and a correct calculation of the different weights and their bulk, the distribution may be made with great exactness.
Removing the anchors where they will stow perfectly clear of the ports, and similar to the sheet and spare anchors, will also leave the round of the bow perfectly clear, and remove every impediment to its being better fortified.
Plymouth, Feb, 14th, 1829.
Geological Notices of St. Helena suggested during a Visit to
that Island in 1828, in a Voyage from India to England.
By CHARLES H. Weston, Esq. The island of Saint Helena is interesting to the visitor on every account. Whether he may view it as the little spot which has formed the last and circumscribed retreat of one who in the days of his glory and ambition thought the wide world scarce sufficiently extensive; or whether he consider its peculiar scenery abounding in contrasts—of luxuriance and sterility, between whose rugged and naked hill-tops and grass-green vallies there is no such gradation as the English eye is accustomed to dwell upon; or whether he look upon its volcanic characters, and reflect upon the period when nature here exhibited such awful proofs of her irresistible power,—it will be found equally capable of exciting his interest. But it is in its last character that we are interested, and about which I would offer some remarks. These remarks, however, must unavoidably be few in number, and somewhat superficial in their nature, from the limited residence which the shipment of necessary supplies usually affords to passengers in their voyage from India to England.
But while stating the characters of the few geological specimens I collected and procured, I shall not hesitate to make use of the information of others, whose opportunities have afforded them better local knowledge; and if any hint should lead other and more able travellers to direct their attention to the geology of this singular island, so as eventually to throw any light upon the interesting problem,“ Whether St. Helena is truly a volcanic product, or the remnant of a much larger portion of land now submerged," *-an object of no small importance will have been attained.
In approaching St. Helena from the southward, we sail
* Vide Beatson's “ Tracts relative to St. Helena.) Daubeny on Volcanoes. Philosophical Magazine, No. 342.
round the island from the south-east to the north-west, so that a great line of coast is presented to our view, and as the shores are so precipitous as to allow a ship to sail within almost two cables' length of the land, the whole coast is distinctly seen and may be easily examined. But I did not in any part recognise rocks belonging to the primitive formation ; neither did I meet with any during my rides in the interior. From General Walker's geological notices * also, it is evident that he had never met with any of this class; and as Governor Beatson is equally silent on this subject, we may conclude that primitive rocks do not exist in the island.
The perpendicular coast seems to give strong evidence of the convulsions which St. Helena must have experienced at some remote period; for not only is it intersected with deep ravines, but at the northern part there appeared to be nearly a complete separation of the cliff from the top to the bottom. The whole stratification also is much disturbed, and dips in every direction; at one spot I recollect seeing the stratą of a hill to dip on either side to the contiguous vallies.
There are many parts which are beautifully intersected by red veins, composed of alumina, highly impregnated with the red oxide of iron.
In speaking of the general characters of St. Helena, I would only remark, that the volcanic matter chiefly consists of a rock of a basaltic naturet; and therefore, when we read, that “ obsidian or pumice has never, I believe, been found here," I we see a reason why the latter substance, at least, should not have been found, as it is the product of trachyte or feldspathic lava, and not of augitic or basaltic lava Ş.
But before describing the interior of the island, I will here subjoin a list of some geological specimens, with their localities:
No. 1, Basaltic lava, compact,
2. Ferruginous schistos,
* Vide Philosophical Magazine, No. 342. of See also Daubeny. I See Philosophical Magazine, No. 342.
See Daubeny, p. 24, et passim. Analysis of different substances in Ure's Chemical Dictionary; and article“ Pumice," Rees's Cyclopædia.
No. 3. Ancient lava (ferruginous)
Ladder Hill. 4. Ancient lava (ferrug is) one side blackened and)
vitrified, with part converted into sponge-form Rupert's Hill.
oxide of iron,
3 and 4, to the cellular of No. 7,
Break-neck Valley. 12. Pitch stone, approaching red jasper
Lot's Wife. 13. Semi-opal (amorphous) $
Gregory's. 14. Indurated lithomarge,
Unknown, 15. Lithomarge converted into a kind of porcelain, 16. Stalactite, s
Sandy Bay. 17. Do. massive, zoned, and agate-like, § 18. Globular aggregated octohedral crystals of sulphate
Sugar Loaf. of lime,
On reading over the above enumeration of specimens, we are immediately struck with this very singular fact :-that St. Helena must have suffered at least three distinct volcunic eruptions. Nos. 1, 3, 4, 5 and 6, 7 and 8, are the specimens here referred to. These lavas were evidently formed not only at three distinct periods, but, as their mechanical texture clearly shews, under totally different circumstances. The effects of heat, in the formation of each lava, have been modified by the influence of pressure. †
The incalculable weight of the ocean superimposed, would effectually prevent the escape of gaseous products, and thereby give to the fluid rocks that dense character and that freedom from porosity, which basaltic lava of this kind (No. 1.) always
* The situations of those marked , are given on the credit of the person from whom they were bought: the rest I collected on the spot. + See the different effects of pressure ably explained by Daubeny.
presents. - Lava such as this could not have been formed without pressure; I would, therefore, denominate it-submarine lava."
The lavas of numbers 3 and 4 appear to be intermediate between numbers 1 and 7 and 8. The grain is close but penetrated with minute pores ; evidently formed under less pressure, which was not quite sufficient to prevent the escape of gaseous products.
It might at first seem that the intermediate lavas had been formed after a partial subsidence of the waters of the deluge, (to which we shall soon again refer); but the specimen marked No. 6, possessing in itself both porous and cellular lava, proves it to have suffered a diminution of pressure, even during its ejection. We are, therefore, rather led to attribute this effect to the more sudden rise of the volcanic island, than to the result of the more gradual removal of pressure, which the first hypothesis would involve.
This lava, also,, was therefore formed entirely under water, although, when compared with the first eruption, atino great depth.
If we thus suppose the two first lavas to have been formed previous to the total subsidence of the waters, the great argument which Beatson derives from the level plains of " Long Wood,"
Dead Wood," and others, against the volcanic origin of this island, will lose much of its force. Under these supposed circumstances, this tertiary formation of “ soil and clay" must have been regularly deposited over this yet submarine land, with its surface necessarily smooth and “ level.” The existence also of “considerable beds of small stones resembling gravel,!!- of which Governor Beatson makes mention, is a collateral proof of the agency of the sea, in the formation of these " Great Plains." *
I shall, for the sake of distinction, term these first lavas antes diluvian; because ejected at least previous to the total subsidence of the waters.
But not till after this event (the total subsidence of the
*« This soil a little north of the Great Wood, is strongly impregnated with salt; nothing grows upon it but marine plants."-Beatson.