At Merstham one of the odd problems of the new line was reached, for there it had to be constructed over a network of ancient tunnels made centuries ago in the hillside--quarry-tunnels whence came much of the limestone that went towards the building of Henry VII.'s Chapel at Westminster Abbey. The old workings are still accessible to the explorer who dares the accumulation of gas in them given off by the limestone rock. The geology of these five miles of new railway is peculiarly varied, limestone and chalk giving place suddenly to the gault of the levels, and followed again by a hillside bed of Fuller's earth, succeeded in turn by red sand. The Fuller's earth, resting upon a slippery substratum of gault, only required a little rain and a little disturbance to slide down and overwhelm the railway works, and retaining-walls of the heaviest and most substantial kind were necessary in the cuttings where it occurred. Tunnelling for a quarter of a mile through the sand that gives Redhill its name, the railway crosses obliquely under the South Eastern, and then joins the old Brighton line territory just before reaching Earlswood station. [Illustration: CHIPSTEAD CHURCH.] All these engineering manifestations give the old grim neighbourhood of Smitham Bottom a new grimness. The trains of the Brighton line boom, rattle, and clank overhead into the covered way, whose ventilators spout steam like some infernal laundry, and from the 80-foot deep cuttings close beside the road, steamy billows arise very weirdly. Presiding over all are the beautiful grounds and vast ranges of buildings of the Cane Hill Lunatic Asylum, housing an ever-increasing population of lunatics, now numbering some three thousand. Sometimes the quieter members of that unfortunate community are seen, being given a walk along the road, outside their bounds, and the sight and the thoughts they engender are not cheering. Along the road, where the walls of the cutting descend perpendicularly, is the severely common-place hamlet of Hooley, formerly Howleigh, consisting of the "Star" inn and some twenty square brick cottages. Just beyond it, where a modern Cyclists' Rest and tea-rooms building stands to the left of the road, the first traces of the old Surrey Iron Railway, which crossed the highway here, are found, in the shallower cutting, still noticeable, although disused seventy years ago. Alders, hazels, and blackberry brambles grow on the side of it, and its bridges are ivy-grown: primroses and violets, too, grow there wondrously profuse. [Sidenote: CHIPSTEAD]