266 



length of about 400 yards in the whole Tunnel) where the rock 

 is so homogeneous, and free from fissures and faults, as to hold 

 the water without clay side lining and walls supporting the 

 same, which are carried above the water level, as shown on 

 Cross Section No. 3. This arrangement is general throiigh the 

 rocking. Similar clay lining is also carried behind the side 

 walls in a great portion of the arching, and a bottom lining of 

 pounded clay, or of clay puddle is continuous throughout the 

 Tunnel, except where it is formed through sound clay in the 

 Fullers Earth. Where fissures in the rock had to be en- 

 countered, doors of oak were fixed across the side walling, 

 and linings into two grooves cut on either side of, and some 

 little distance from such fissures into the rock, so as to block 

 the flow of any side leakage towards such fissures, which 

 probably answered very well at the time; but these wooden 

 doors have since occasioned much trouble. In consequence of 

 the decay of the timber, cavities have been formed where they 

 existed, and the leakage, which it was intended to prevent, has 

 been aggravated by them. 



Where bottom springs enter the Tunnel, and in other bad places, 

 large trunks made with 2^ inch thick planking at the bottom, 

 and 2^ inches thick at the sides, were designed, as shewn on the 

 Cross Section No 4, &c., to carry the Canal.* Every expedient 



* The Engineer's Specification of the work for this Trunking is as follows : — 



The Planking is to be put on the thickness ordered, and the seams to be 

 well caulked and pitched like the sides of a ship. The Planks to be fixed on 

 with trunnels and spikes. 



At difi'erent distances, according as the holes of the springs have at any- 

 time appcai'cd, trunks of 10 inches square inside (made of 2-inch oak plank) 

 must be constructed and fixed cross the floor, from the orifice of the said 

 springs and up the sides behind the side planking, with discharging mouths 

 like the nozel of a pump ; so that the water of the said springs may discharge 

 their produce 3 inches above the water level of canal, and not to diink any 

 out of it. 



Between the sleepers or cross timber well-tempered clay, not over wet, must 

 be ram'd well down and under each breadth of plank as the work advances. 



Walling of brick or stone must be built between and behind the side 

 timbers, for the purpose of steadying the framed work of the sides from any 

 blows or thumps of barges ; and the said walling must be carried up and 

 over the side rails untd that work meets the incumbent rocks of the ceiUng 

 where it is not arched. 



