No. 10.Top of barrack
No. 10.
Various conjectures were made as to the cause of the destruction of the barrack. Those who saw it erected were so confident of its stability, that they could not avoid connecting its failure with some injury received from the wreck-timber, which had come ashore on the island of Tyree, two days after the supposed date of the accident. In this opinion they were strengthened by the total destruction of the cranes and other objects on the rock, forgetting that the timber of the barrack itself, when once let loose, must of necessity have proved even a more powerful agent of destruction than the driftwood of the wreck. But whatever doubt may exist as to theCause of the destruction of the barrack.first cause of the injury, there seems good reason to suppose that the dismemberment of the parts of the structure had commenced with the removal of the horizontal braces, and that the beams, having thus more liberty for play and tremor, had gradually shaken loose the fixtures at the top, which consisted of strapscc, passing right over the topsaa, of the beams andb b, the hexagonal quoin of hardwood already noticed atp. 88, which were secured by means of a central boltd, and finally girt outside by a ring,ee, as shewn in the annexed woodcut (No. 10.) The moment this dismemberment occurred, the beams would be free to work their own destruction; and the enormous leverage which they exerted, when dashed to and fro by the breakers, would soon snap the iron stancheons at the base, and throw all loose to the waves. The only remaining beam was that which was supported against a ledge of rock, and which had received the sea from the opposite directionto that in which it was found lying. That beam, however, although firmly lashed to the rock by the men who first visited it after the accident, along with Mr Charles Barclay, also disappeared in the course of the winter. As a proof how severely these beams had been dashed by the waves, I may state, that the only remaining part of a beam which I saw attached to the iron stancheons, when I landed in the following spring, was so thoroughly riven andshakenas to be quite like a bundle of lathwood.
No. 11.
No. 11.
These circumstances by no means shook my belief in the suitableness of the plan adopted for obtaining a temporary dwelling on the rock; but they induced me, as soon as I received authority from the Commissioners, whose confident expectation of final success was not damped by the unhappy issue of our season’s labours, to examine very carefully the whole details of the ties and fastenings.Preparations for a new barrack.In preparing a similar structure for next season, I resolved to strengthen the ties at the top, where I imagined the former failure to have occurred, by adding six strong stancheonsa,a(Plate V.), one to each beam, with heads passing through a centre-plate (H), which united them in one as a cap and to which they were secured by strong screws and keys. The nature of those fixtures will be more easily understood by a reference to the figures (1) and (2) inPlate VI., which shew an elevation and plan of the upper part of the beams. In the elevation only the beams A, B, C, are shewn; but in the plan, all the six beams appearmiteringat their headsn,n, to the central beam or tieo,o(see alsoPlate V.), which was introduced to counteract the tendency of the heavy seas that might burst inside the pyramid, and by exerting a powerful force in the vertical direction, might separate the beams at the top. In thePlate (VI.),a,a, are strong stancheons of iron attached to the outside of the beams by bolts, and also by collarsr,r, attached to earsg,g. These stancheons being bent into the vertical direction and rounded at the top, passed through the malleable iron plate H, which was held down, and, as already stated, bound the beams together by nutsc,c, and wedgesb,b. Through a hole in the centreof this plate, a large spikepwas driven, which produced an expansion of the central beam, and thus wedged up or tightened all the joints formed by themiteringof the seven timbers. On each of those stancheons,snugswere formed ate, capable of receiving and retaining in its place against any tendency to move upwards, a strong metallic ringg, which was tightly keyed by wedges atk. Additional ties of iron D, E, F, were also provided, which connected the six beams together in pairs. Each end of those ties was attached to the timbers by three spikes; one tie, D, is shewn a little fore-shortened; another, E, is seen only on the end; while the third F, is shewn as cut off at the middle. Lastly, an important change was made, by the substitution of malleable iron for wooden braces (seePlate V.)b,b,b,b, in the horizontal direction. Fixtures of this kind held the whole more firmly together; and their construction was such that they might firmly embrace each beam, without requiring any means of attachment beyond wedging tightly up; and thus the entire strength of the timbers was unimpaired by the driving of spikes or bolts. Those braces (No. 11),a,a, had, at each end, double knobs, and were pushed up along the beams, until they squeezed the timbersx,x,xbetween them; platesp,p(having holes in them through which the double knobs of the braces were made to pass), were then put on and keyed and screwed, as shewn in the figure, sothat each beam was quite enclosed by fixtures, which were thus independent of spikes or bolts. Thin hardwood wedges were afterwards driven in, wherever they could be inserted between the iron and the timber; and those wedges were “stitched” to the beams with common nails, merely to prevent their dropping downward, after any temporary contraction of the timber from the state of the atmosphere. In all this, I have anticipated what more properly belongs to the works of the season 1839; but I consider it best, for the sake of clearness, to connect this account of the new with the destruction of the old Barrack.
While the operations already described were in progress at the Rock,Works at Hynish.various works were going forward at the workyard in Tyree. About 16 masons, 12 quarriers, and 4 carpenters, were employed in building the barracks for the workmen and in erecting smiths’ and carpenters’ shops. A large room, paved with a stone floor, for drawing out at full size the courses of the Tower and making the moulds for dressing the stones, was also provided; and a platform of squared masonry was set in the workyard, on which the courses were to be laid, before being shipped for the Rock. During the season, the pier had also been carried out 256 feet, to a point 15 feet within the low-water mark. It was also necessary to provide depositories for the security of tools and other implements, as well as a large coal-shed for the supply of the Steamer which was then in the course of being built. It had, as already noticed, been determined that the stores were to be served out at the cost prices of the Greenock market, to be paid for once a month, at the same time that the wages of the men were paid. That arrangement had been carried into effect on a small scale, from the very beginning of the works; but this season it became necessary, owing to the increased number of men, to conduct it on a more extended and systematic plan; and, for that purpose, a person was required to act as storekeeper and clerk. In order also to preserve the provisionsfrom injury by damp and to secure them from the inroads of the needy Celts and from innumerable rats which overrun that part of Tyree, it was found necessary to set apart, as a storehouse, a large room on the second storey of one of the workshops. The chief articles served out in the store were meal, molasses, sugar, coffee, tea, tobacco and butter. The establishment of the store entailed a great deal of trouble, and led to some expense for carriage and packages, as well as to occasional trifling losses in serving out the allowances or from injury sustained in the transport of the goods; but the inhospitable nature of the country, and the remoteness of Tyree from the ordinary steam-boat traffic, made the adoption of some such plan unavoidable. Amongst other inconveniences which attended the store, not the least may be reckoned the frequent importunities, on the part of the native labourers whom we employed, to be permitted to purchase provisions at the workyard; but that was never acceded to, except in cases where dearths (which are of frequent occurrence in the island) rendered the call irresistible. Had their entreaties easily prevailed, we should soon have had the whole population of Tyree as our regular customers at the Store.
Hynish Quarries.The quarries at Hynish, as already stated, were by no means productive. The great proportion of the materials which had been quarried, was found to be applicable only to the building of the pier and the inclosing walls, and to the various erections in the workyard; and not more thanone-tenthof the whole could be dressed as blocks for the Tower.
During the numerous occasions on which I had been driven by stress of weather to the neighbouring coasts, I had visited the quarries around Oban and in various parts of Morven and Mull. When so forced to leave what I might more especially call mypost, I had an opportunity of seeing the quarries at Ardentallen near Oban, which contain the old red sandstone strongly impregnated with clay. That stone is by no means suitable for theface-workof a marine building, in such a situation as the Skerryvore; while the comparatively small quantity ofheartingwhich could be admitted into such a work, made it inexpedient to seek such materials at so great a distance. In this way, the Ardentallen quarry seemed completely excluded from the field. At another time, in passing through Inverary, I devoted a day to the examination of the quarries which had lately been opened at that place and in which a beautiful porphyry is wrought; but I saw no appearance of very large blocks, or, at all events, nothing that could favour the expectation of a considerable supply. But after carefully weighing the matter, the great masses of granite at the Ross of Mull finally determined my choice in favour of that locality; and the Duke of Argyll having, with the greatest liberality, ratified his predecessor’s grant of liberty to the Lighthouse Board to quarry stones from any part of the Argyll estates, it was resolved to take measures early in the spring of 1839 for opening quarries at North Bay, in Mull, where an excellent station for shipping had been discovered, close to the place where we saw the most promising appearance of rock. This measure seemed the more indispensable, as the last part of the quarryterred[18]or laid bare at Hynish, had greatly disappointed our expectations. The unworkable nature of gneiss rock also and its extreme uncertainty with regard to quality, farther concurred to make a change most desirable. Granite, indeed, is a material in many respects superior to sandstone, gneiss, or porphyry. The first it greatly excels in durability and weight; and, as a stone for the workyard, it is superior to the other two, from its property of beingfissile, or easily split in any direction. In this respect it resembles certain parts of some sandstone strata which are commonly calledliverrock, of which Craigleith quarry, near Edinburgh, furnishes an excellent example. Porphyry, and, I think, all other igneous rocks (excepting granite), gneiss also, and most of the other primary rocks, have not this property, beingfissileonly in one plane, so that quarries of those rocks generally turn out very uncouth or irregular stones, which, though they may in some favourable cases possess good naturalbeds, will always be found to have ragged and irregularjoints, which, for the most part, are incapable of being properly dressed.
[18]This term in Scotland denotes the removal of the soil and unsolid material, in order to lay bare the rock previous to working the quarry, and seems obviously to be derived from the Latin “terra,” perhaps through the medium of some old charter. The quantity of terring very much affects the profitable working of a quarry.
[18]This term in Scotland denotes the removal of the soil and unsolid material, in order to lay bare the rock previous to working the quarry, and seems obviously to be derived from the Latin “terra,” perhaps through the medium of some old charter. The quantity of terring very much affects the profitable working of a quarry.