108 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[March, 



accliiily is niori' piaduul ; and lieru, nil acioiiiil of gra\ullY carlh btiiig 

 readily procured from the adjacent bank, it was found most eeoiioiiiical to 

 push forward an eartlien embankment, 1,500 feet in length from the le^■el 

 of the -nater-wav of the canal, until its perpendicular height liccame 75 

 feet; still a distance of 1,007 feet inleneiied before arriving at the north 

 bank, and in the middle of this space the river Dee was 127 feet below the 

 water level of the canal, which was to be carried o^ or it ; therefore serious 

 consideration was requisite in what manner to accomplish this passage at 

 any reasonable expense. To lock down on each side 50 or 60 feet, by 7 or 

 8 locks, as originally intended, I perceived was indeed impracticable, as 

 involving serious loss of water on both sides llie valley, whereas there was 

 not more than sufficient to supply the imavoidable lockage and leakage of 

 the summit level. To construct an aqueduct upon the usual principles, by 

 masonry piers and arches 100 feet in height, of sutiicieiit breadth and 

 strength to afl'ord room for a puddled water-way, would have been hazar- 

 dous, and enormously expensive : necessity obliged nie therefore to con- 

 trive some safer and more economical mode of proceeding. I had about 

 that time carried the Slirewsbury canal by a cast-iron trough at about 16 

 feet abo\e the level of the ground; and linding this practicable, it occurred 

 to me, as there was hard sandstone adjacent to Pont-y-cysylte, that no very 

 serious difficulty could occur in buildmg a number of square jiillars of suf- 

 ficient dimensions to support a cast-iron trough, v\ith ribs under it for the 

 canal. Afler due consideration I caused a model to be made of two piers, 

 a set or compartment of ribs, the canal trough, the towing-path, and side- 

 railing, with all the flanches, tlieir nuts and screws and jouiting complete. 

 The loiuidatioiis of the river piers arc placed upon hard sandstone rock ; 

 those on each bank are either on alternating coal strata, or hard firm gra- 

 vel. Thus secure of good foundations, suitable sandstone for the masoniy, 

 the best of iron, a satisfacloiy model of the iron work, and able experienced 

 workmen, I proceeded with conhdeiice of ultimate success, although tho 

 undertaking was unprecedeuled, and generally considered luizardous. 



" The height of the piers above the low water in the river is 121 feet, 

 their section at the level of high water in the river is 20 feet by 12 feet, 

 at the lop 13 feet by 7 feet 6 inches. To 70 feet elevalioii (ioin the base 

 they are solid, but the upper 50 feet is built hollow; the outer walls 

 being only 2 feet in Ihickness, with one cross inner \\'all ; this not only 

 places the centre of gravity lower in the pier, and saves masonry, but insures 

 good workmanship, as every side of each stone is exposed. " I have ever 

 since that lime caused eicry tall jiier imder my direction to be thus buill. 

 The \\idtli of the v\ater-way is 11 feet 10 inches, of which the lowing-patli 

 covers 4 feet S inches, lea\ing 7 feet 2 inches for the boat; but as the 

 towing-path stands upon iron pillars, under which (he water flucluates and 

 recedes freely, the boat passes witli ease. The stone piers are 18 in num- 

 ber, besides the two abutment piers ; they were built to the level of 20 

 feet, and then the scaflblding and gangways were all raised to that level, 

 and the materials being brought from the liorlh bank, the workmen always 

 commenced at the most distant or soutli aliutmeiit pier, receding pier by 

 pier to tho nortli bank ; and by thus ascending IVoin time to time in their 

 work, they felt no more apprehension of danger when on tho lughest, tlian 

 at first on the lowest gang-ways ; one man only fell during the whole of the 

 operations in building the piers, and affixing the iron work upon their sum- 

 mit, and this took pla<-e from carelessness on his part. 



'■ By referring to Plate 14, the general fonn, and also the details of con- 

 struction, will be readily vmderstood. Tliis singular aqueduct was opened 

 in 1805, and has now been navigated 28 years with facility and safety ; and 

 thus has been added a striking feature to the beautiful vale of Llangollen, - 

 111 which formerly was the fastness of Owen Glyndwr, but which, now : 

 cleared of its entangled woods, contains a useful line of intercourse between 

 England and Ireland ; and the water drawn from the once sacred Deva, 

 hmushes the means of distributing prosperity over the adjacent land of the 

 Saxons. 



"Tho whole expense of the aqueduct, and great embankment, was 

 £47,018 ; a moderate sum as compared v\ith what by any mode herc'tofore 

 in practice, it would have cost." 



Telford had now sufRcient standing to recommend him for the exe- 

 cution of great works, and sufficient ability to justify the choice, and 

 we consequently find Ifim employed on (he Caledonian canal. This 

 was one of the political lions of the day, and many exjiectations were 

 formed of the utility of this national iinckrlaking ; but except forming 

 a fertile source of government and local jobbery and an interminable 

 sink of Englisli money, it has produced nothing but disappointment 

 and disgrace. We shall endeavour to give some explanation of the 

 causes whicli led to this, and from our own sources point out the 

 reasons for its defeat. To understand the subject better, however, it 

 IS necessary that the reader should understand somethino- of the 

 nature of the countiy, which is explained in the following extracts, 

 describing a singular valley, 



" Called the Great Glen of Scotland, which, commencing between the 

 promontory of Burgh-Head in Elginshire, and Cromarty, passes through a 

 succession of sea-mlets and fresh-water lochs (lakes) to the southerir ex- 

 tremity of Cantyre, a distance of 200 mUcs, and in nearly a straight direc- 

 tion between the Naze of Norway and the north of Ireland. Tlie 

 whole of this extensive valley, with the exception of about 22 miles, being 

 occupied by navigable waters, and the excepted space by a navigable canal, 

 ^avcs upwards oi 500 miles of dangerous navigation, as compared with that 

 by the Orkneys and Cape Wratli, ,';liips of «ar, were this track open to 



them, might in two days, from a station at Tort George near Inverness, 

 reach Ihc north of Ireland." 



The description of the works on the canal is meagre in the extreme, 

 deficient in interest, and destitute of tliat practical instniction which 

 such immense works might have afforded. Numerous difficulties 

 were to be encountered and overcome, and, as Telford liimselfob- 

 serves, the narration of failures often leads to more practical informa- 

 tion than the description of succes.s. From the account of the Cale- 

 donian Canal we shall give a few extracts, whicli may serve to 

 explain the comments we have to make thereon. 



" About ten miles within Fori George, and one mile to the north-west 

 of the mouth of the river Ness, the tide-way of the Beauley Water is from 

 5 to 7 fathoms deep, and here, at the fishing village of Clacluiacharry, is the 

 entrance of the Caledonian Canal. In order to secure an entrance for ves- 

 sels of 20 feet draught of water, at the top of neap tides, it was nei^essary, 

 from the flatness of the shore, to place the tide-lock 400 yards from 

 liigh-water mark, at the end of an embankment ; and in constructing this 

 lock, very considerable difficulties occuiTcd. wliich will be afterwards 

 described. I shall here only observe, that this sea or tide-lock is 170 feet 

 long in the chamber and 40 feet wide, and that its rise is 8 feet; from this 

 lock the canal is formed by artificial banks, upon a flat mud shore, uiilil it 

 reaches high-waler mark at Clachnacharry, where another lock of similar 

 dimensions is pla<'ed upon liard mounlain clay. Immediately to the soulli 

 of this, is formed a basin or floating dock, 067 yards in length and 162 in 

 bicadth'; it.s area is about 32 English acres. It is furnished with a wharf- 

 wall and warehouse at the south end, and its ample dimensions produced 

 earth by excavation for its own banks, and also for supporting the adjoin- 

 ing locks, instead of having recourse to back-cutting. 



" At the soulli end of this basin, the great north road passes over a 

 swing bridge, and adjacent to it are tho four miited Muirtown locks, each 

 180 feet 'oiig and 40 feet wide, which together rise 32 feet, lifting the canal 

 to the level of the surface water of Loch Ness, when in its ordinary summer 

 slate. From the lop of these locks the canal, 50 feet wide at the bottom, 

 20 feet deep, and 120 feet at surface water, is carried by easy bends in tlie 

 rear of the insulated hillock of Tomnahuric, to the river Ness at Toriaine, 

 where, by reason of a precipitous liank, the canal is constrained to occupy 

 the former bed of the river, a new channel being made for it by removing 

 the opposite bank, which at the same lime produced earth for separating 

 the river and canal ; a gi'eat work, more than half a mile in length. The 

 same kind of difficulty, but less in extent, is overcome in the same maimer 

 twice before the canal enters the small loch of Doughfour, (six miles from 

 Clachnaclmrry) by a regulating lock 170 feet long and 40 feet wide, actually 

 placed in the old channel of the river Ness, which in this place was hereto- 

 fore separated uito a double stream by an island of gravel. .Such a situa- 

 tion points out the difficulty of keeping an extensive lock-pit free from the 

 influx of river water, the ordinary level of which was 20 feet above tho 

 necessary excavatii>u. Mr. Davidson's incessant attention was necessary 

 and conspicuous during tliis unusual operation in the years 1813 and 1814, 

 as well as that of Messrs. .Simpson, Cargill, and Rhodes. 



" Between the small Loch of Doughfour and the outlet of Loch Ness at 

 Bona Ferry, the river has been deepijped, chiefly by a dredging machine. 

 Loch Ness is about 22 miles in length, no where less than a mile in breadth ; 

 in depth varying from 5 to 120 fathoms, (a greater depth than is found 

 between the Murray Firth and the Baltic sea,) its direction is straight, with 

 several small bays of moderate depth, aft'ording good anchorage, as at 

 UrqiUiart, Inverniorrison, and Port-Clare, on the north side ; taiid at Dores, 

 the fall of Fyers, and the Horse-shoe on the south side. 



'' At the south-west end of the Loch stands Fort-Augustus, on the north 

 side of which the river Oich enters Uie Loch where the canal leaves it, 

 crosses the glacis, and at the back of the village ascends 40 feet by means 

 of five connected locks, each IsO feet in length ; from thence it passes along 

 the south side of the river to the norlh-east corner of Loch-Oich. In this 

 distance of about five miles is the Kytra lifting lock, and a regulating lock, 

 each 170 feet long and 40 feet w-ide, and the channel of the river has been 

 changed in two idaces; the breadth of Loch-Oich is inconsiderable and 

 irregular ; in some parts it requires deepening by dredging, especially 

 where the river Ciarry falls in from the north, draining the whole of Glen- 

 garry', and ha^■iIlg in its course Loch-Garry 6 miles in length, and Loch- 

 Quoicli 10 miles ; the summit supply of water for the Caledonian Canal is 

 therefore abundant. 



'■ Between the western end of Loch-Oich and the east end of Loch- 

 Lochy, a distance of about two miles, the surface of the ground is about 

 20 feet above the water level, and the depth of the canal water being 20 

 feet, there is 40 feet depth of cutting. Near Loch-Lochy are two locks, a 

 regulating lock and a lifting lock ; the diflerence between the surface of 

 the water in these two locks (.although Loch-Lochy has been raised 12 

 feet,) is nearly 10 feet. 



" At the south-west end of Loch-Lochy (which is 10 miles in length) 

 there is a regulatuig lock as usual, and the canal is carried over rugged 

 ground along the north-west side of the river Lochy, its line intersected by 

 one considerable riier, and by scleral momitain streams ; tho ordinary 

 level of Loch-Lochy is continued along the canal to within one mile of 

 Loch-Eil, where are eight coimected locks, each 18tl feet long and 40 feet 

 in width, and together falling 64 feet ; from thence the canal is continued 

 on a level to Corpach, where are two connected locks falling 15 feet, and a 

 single sea-lock entering the tideway of Loch-Eil. The sill of this last- 

 niciiiioned lock was laboriously excavated iii rock, so as to ensure a depth 



