CHAP. XV. KILSBY TUNNEL. 315 



rapidly. Hence an unusual thickness of brick lining 

 was found necessary ; and the engineer afterwards 

 informed the author that for some time he entertained 

 an apprehension lest the pressure should force in the 

 brickwork altogether, as afterwards happened in the 

 case of the short Preston Brook tunnel upon the Grand 

 Junction Railway, constructed by his father. He stated 

 that the pressure behind the brickwork was such, that it 

 made the face of the bricks to fly oif in minute chips, 

 which covered his clothes whilst he was inspecting the 

 work. The materials used in the building were, how- 

 ever, of excellent quality ; and the work was happily 

 brought to a completion without any accident. 



At Watford the chalk ridge was penetrated by a 

 tunnel about 1800 yards long; and at Northchurch, 

 Lindslade, and Stowe Hill, there were other tunnels of 

 minor extent. But the chief difficulty of the undertaking 

 was the execution of that under the Kilsby ridge. 

 Though not the largest, this is in many respects one of 

 the most interesting works of the kind in this country. 

 It is about two thousand four hundred yards long, 

 and runs at an average depth of about a hundred and 

 sixty feet below the surface. The ridge under which 

 it extends is of considerable extent, the famous battle 

 of Naseby having been fought upon one of the spurs of 

 the same high ground some seven miles to the eastward. 



Previous to the letting of the contract, the character 

 of the underground soil was fairly tested by trial shafts, 

 which indicated that it consisted of shale of the lower 

 oolite, and it was let accordingly. But the works had 

 scarcely been commenced when it was discovered that at 

 an interval between the two trial-shafts which had been 

 sunk about two hundred yards from the south end of 

 the tunnel, there existed an extensive quicksand under 

 a bed of clay forty feet thick, which the borings had 

 escaped in the most singular manner. At the bottom of 

 one of these shafts the excavation and building of the 



