574
HISTORY OF ENGINEERING.
Hook I.
with a strong double railroad upon it, to receive boats with their carriages. When theboats arrive at this height, with their load of live tons, they pass along a level canal for Qmiles, and then descend by an inclined plane, 600 yards in length, and 126 of perpen-dicular height; they then, by another level line of canal, which is the summit, proceed toRodwardine Wood inclined plane, which is 320 yards long, and 120 feet perpendicularfall. Other inclined planes succeed; the whole works were completed in 1792.
Somersetshire Cool Canal commences at Limpley Stoke, in the Kennet and Avon canal,and terminates at Paulton.
Staffordshire and Worcestershire Canal . — From the river Severn at Stourport, and uniteswith the Trent and Mersey navigation, near Haywood in Staffordshire . Aqueducts con-duct it over the river Trent and Sow Penk, Smester and Stour; there are also three tun-nels, one under the town of Kidderminster .
Stamforth and Keadby Canal, from the Don at Fishlake, to the river Trent at Keadby inLincolnshire .
Stourbridge Canal . — From Stewponey on the Staffordshire and Worcestershire canal toStourbridge .
Stafford-upon-Avon Canal commences at King’s Norton, and at 6 miles from Birmingham joins the Worcester and Birmingham . It has four branches, one to the Tamworth quarries,2£ miles long, another to the Warwick and Birmingham canal, 1^ miles long, and one atTemple Grafton Lime Walks, 4 miles in length, and the other 1 mile in length to AstonCantslow. Near Milepole Ilill is a tunnel, 320 yards in length, and several smallaqueducts.
Swansea Canal, from the harbour, where the Tawe river falls into the Pen Tawc.
Tavistock Canal, from the tideway of the Tamar, at Morwelham Quay Basin, to Tavi stock . Under the Morwelham dam is a tunnel, 2646 yards long ; this tunnel has 460 feetheight of earth and rock above it. The locks are made for boats 12 feet 6 inches long,and 5 feet wide. At Crebar there is an aqueduct 200 yards long, and 60 feet above theriver.
Thames and Medway Canal commences at Gravesend , and by a tunnel through the chalk,it enters the Medway at Frinsbury.
The chalk formation,through which this tunnelis driven, was by no meansfavourable to its exe-cution : in some places itwas found so soft that itcrumbled before the miner,and in others so dense thatit was necessary to blastit with gunpowder; wherethe chalk was mixed withveins of earth, it requireda considerable number ofstout yellow pine spars9 inches in diameter tosupport it; these were fre-quently crushed beneaththe weight to which they were opposed, and some serious accidents occurred. The thick-ness of the brickwork varied according to circumstances: at the summit of the tunnel itwas 14 inches, and generally at the springing 18 inches. The space above the brick archwas filled in with chalk and lime mortar as the vaulting advanced, and the chalk abovewas pinned up as securely as possible.
The length of the tunnel is 2^ miles, and the entire length of the canal nearly 7 miles;the passage round the Nore and up the Medway is thus avoided, and a distance of nearly50 miles saved in the navigation.
Whilst this tunnel was in progress the water in the surrounding wells, for a very con-siderable distance, sank so low that it was necessary to deepen them to obtain a supply.When the salt water was admitted into the canal it affected all the fresh which pervaded thechalk district, and materially injured the quality of that which was drawn from the newlydeepened wells, and great expense was incurred by the company, who were assessed inconsiderable damages for these injurious effects. The entrance from the Thames atGravesend is through a basin ; the canal is 50 feet wide and 7 feet deep to where the tunnelcommences, a distance of 4^ miles. Mr. William Tiernay Clark, the engineer, commencedthe works in April, 1819. The width of water-way in the tunnel at top is 21 feet 6inches, and at bottom 20 feet; the depth is 8 feet; the towing-path is 3 feet above thewater, and 6 feet higher the footing of the brick arch, the clear width of which is about 30feet; the occasional perpendicular shafts arc 8 feet in diameter.