The one hundred eight foot keystone arch tunnel, the longest in Connecticut, located on Tunnel Road, is an outstanding example of the stonemason's art. Built between 1846 and 1849, by masons and stonecutters, many newly arrived from Ireland, with only the help of oxen and hand tools, it is a marvel of engineering skill.
The sudden rise in elevation from the level sandstone valley at Vernon Depot to the hills of Connecticut's eastern highlands in Bolton proved a problem to the men who set about laying the first railroad tracks from Manchester to Bolton Notch. To provide the gentle incline necessary for the trains to ascend, a tremendous amount of earth fill had to be brought in and tamped into place. In order not to block the then long-existing road from Lake Street to Vernon Center this tunnel was constructed. To do this a strong, temporary wooden frame, called a "central", the exact size and shape of the finished vault was built . This held the weight of the inward leaning side stones until the keystone at the top of the arch was firmly set in position.
This keystone thrusting downward on each side pressed the side stones of the arch more tightly together. At this point the wooden scaffolding which had been holding the weight was removed.
This tunnel is made up of thirty arches. Native sandstone from the quarry on Box Mountain was cut and set in each inner arch as carefully as for those facing its two entrances. Mounds of earth on both sides were needed to support the thrust at the base of the walls and the tracks on the roadbed above, along which rains have passed for over one hundred twenty one years.
At its opening the tunnel is fourteen feet wide at its floor and sixteen feet high up to the base of the keystones. Each arch is composed of nine stones on either side of the keystone, supported by five blocks, some as much as five feet long and one and one-haIf feet in height and width. Its retaining wall is made up of forty to forty-five huge sandstone blocks arranged in a stair-like formation Two courses of stones rest above the arches surmounted by a twenty foot four-part capstone.
Along the inside corridor of the tunnel not a crack nor falling stone is in evidence and the walls themselves silently speak of the pride in their workmanship those early craftsmen felt, for high on the vault's sides are carved the initials of many of those who toiled here. Near the north entrance, four blocks up and four in is carved the whole name, "GRADY, JERRY", a mason who settled on Lake Street in 1854.
This venerable tunnel, sometimes referred to as the 'Keyhole Tunnel" stands not only as a fine piece of architecture but as a monument to the integrity and honest workmanship of Vernon's forbears.