[6] Another of the early plans had been to build the whole line across the Blue Mountains on a completely different route through the Grose Valley with a 3-kilometre-long (1.9 mi) tunnel, but this was beyond the resources of the colony of New South Wales at the time.

[4] The line of track (now without rails) goes through well executed rock cuttings on the standard walk along Top Road from Knapsack Street and Skarratt Park.

[7] The culvert, which is still in operation, utilises a rock-cutting on the west side to divert run-off water deep under the track in a square channel constructed of stone blocks.

[4] To the west of the Upper Road there is a series of low sandstone terrace walls which probably marked the boundary between Lucasville estate and the railway.

At the southern entry to the Top Road of the Zig Zag, at the end of Knapsack Street, there is a gate to inhibit vehicle access.

Although Tredwell died in 1859, his widow saw the half Zig Zag to completion in 1863, employing 42,000 men, and this feat was reported at some length in The Sydney Morning Herald on 3 July 1863.

Whitton knew of the conquering of the Bhore Ghat, which posed problems very comparable to the Lapstone Monocline, both from personal and public communications.

The way in which he adapted the Indian experience into a full Zig Zag, approached over an exquisite, and very cheap, sandstone viaduct, was a substantial feat in world terms of railway engineering.

[2] In 1890 signal boxes were built at both Lower and Upper Points of the Zig Zag, this was to replace the operation of pointsmen using hand levers.

The Lapstone Zig Zag and Lucasville station were officially closed on 18 December 1892 and the rails were raised, after the completion of the Glenbrook Tunnel Deviation.

Construction of the Knapsack Gully Viaduct started in March 1863 by contractor W. Watkins, who also completed the stone piers of the Victoria Bridge at Penrith.

Work was completed in 1865, with the bridge being constructed from local sandstone quarried in the neighbourhood around Lapstone and carried a single rail line.

The board sought to improve the route of the Great Western Highway between Emu Plains and Blaxland, that at the time zig zagged up Mitchell's Pass which replaced Old Bathurst Road in 1832.