McMahon's Spadeworks, Tonity Bog, Rosslea, Co. Fermanagh, BT92 7LZ

McMahon's Spadeworks is a 19th-century water-powered spade mill complex located on the north side of a minor road at Tonity Bog, Rosslea, County Fermanagh. It comprises three blocks of buildings, all now in ruinous condition.

The site has significant historical importance. A single-stone water-powered corn mill operated here in the 1830s, belonging to Johnston Lipton and probably dating from the 18th century. By the 1860s, a spade mill had been established alongside it under the ownership of John McMahon. Local tradition suggests the spade mill was erected in the late 1830s or early 1840s, before the Famine. The complex became known as Shannock Mills and remained in McMahon family hands, passing to Patrick around 1877 and James around 1905. The corn mill ceased operations in the early 1900s. Around the First World War, the McMahons opened two additional spade mills—one in Lacky townland, 2 kilometres south-west, and another at Drumard just over the border in County Monaghan.

Block 1 is a single-storey, single-bay spade mill aligned north-south at the east end, positioned on the left side of the mill race. It has a pitched corrugated asbestos roof with chimneys on both gables; the southern chimney no longer has a fireplace and may be ornamental. The walls are random rubble sandstone with no rainwater goods. The principal elevation faces east and contains three openings—a window, door, and window. The south gable is abutted by a lower lean-to shed with monopitched corrugated metal roof sloping south and timber-framed walls; the exposed gable section has window openings on each side. The north gable has a shuttered window at right. The west elevation is blank except for an external waterwheel at the south end. The wheel is high breast-shot, 3.35 metres in diameter by 1.22 metres wide, constructed entirely of timber except for a cast-iron hub and rims. It has six arms per side and originally carried 30 angled buckets, all now missing along with the sole plate. The remains of a sluice gate survive directly above.

Block 2 is located on the opposite side of the mill race and comprises five contiguous sections: the mill proper in the middle, a blacksmith's shop at the north-east, two small offices to the south, and a shed at the north. All walls are wet-dashed over random rubble. None of the openings retain their original fittings, and all window openings have stone cills. The brick reveals to all openings suggest a mid-19th century construction date. The mill proper is two-storey, single-bay and aligned east-west, with a curved corrugated metal roof now mostly gone. The west gable has doors to ground floor and first floor; the latter is accessed by a cement-rendered external stairway and concrete balcony. The north elevation is abutted on its left and middle sections by the blacksmith's shop and shed respectively, with internal connections. The exposed right section has a ground-floor window opening. The east gable has an external waterwheel, a small ground-floor opening at left, and a 4/4 sliding sash at first floor. The south elevation is abutted by the two offices; an internal connection to the right-hand office from the mill probably housed a pulley belt.

The external waterwheel on Block 2's east gable is high breast-shot, 4.27 metres in diameter by 1.14 metres wide, constructed of timber except for cast-iron hub and rims. It has eight arms per side and originally carried 32 angled buckets, all now missing along with the sole plate. The remains of a sluice gate survive directly above, complete with a control mechanism accessed from the ground floor of the mill. This represents a key difference from other known spade mills: the bellows associated with the hearths at McMahon's do not appear to have been water-powered, whereas at the comparative example re-erected at the Ulster Folk & Transport Museum at Cultra, they are powered by a second wheel.

The blacksmith's shop attached to the east end of the mill's north elevation is single-storey, single-bay with a monopitched corrugated asbestos roof sloping down to the east. A small square chimney rises from the north-east corner, with vestiges of a second on the west wall. Brick quoins appear on the upper section of the wall at the north-west corner. The north gable has a door and window; the east elevation also has a window.

A one-storey, one-bay office aligned north-south abuts the left half of the mill's south wall. It has a pitched natural slate roof, partly collapsed, with the remains of a chimney on the south gable. There are no rainwater goods. The south gable has a door at left, a window to right, and a small opening to the apex. The left cheek has a window with the head missing. The right cheek is abutted by a smaller office.

A second one-storey, one-bay office abuts the south-east corner of the mill, with a monopitched corrugated metal roof sloping down to the east. The south elevation has a window to the left (without cill) and a door to the right. The east elevation is blank.

A small one-storey, one-bay shed abuts the middle section of the mill's north wall. A ghost of its monopitch roof (sloping down to west) survives on the mill wall. The west and north elevations are open-sided, with the roof supported on random rubble and mass-concrete piers.

Block 3 is a one-and-a-half storey, three-bay blacksmith's shop and house aligned north-south at the west end of the complex. The south and middle bays have a relatively recent pitched asbestos sheet roof; this is a recent insertion, with the side walls of these two bays and the south gable having been raised in concrete from one-storey height to match the eaves level of the dwelling in the north bay. The roof of the north bay is now mostly missing, but was formerly pitched natural slate. Two brick chimneys—one to each party wall—remain, along with half-round asbestos gutters. The walls are wet-dashed random rubble sandstone. Unless otherwise stated, none of the openings retain their original fittings; window fittings to the south and middle bays were probably shutters. All window openings have stone cills. The principal elevation faces east. The left (south) bay has a window at left and door at right. The middle bay mirrors the south bay arrangement. The right (north) bay has a window and door to ground floor and a 2/2 sliding sash to first floor. The north gable is blank. The west elevation has a window to each floor of the left (north) bay and a window to each of the remaining bays. The south gable has a small infilled opening to the apex.

McMahon's Spadeworks is one of approximately 50 spade mills that once operated in Northern Ireland. The distinctive Ulster spade design meant that about 90 per cent of all Irish spade mills were located in Ulster. The only other complete example known to survive, formerly at Coalisland, has been re-erected at the Ulster Folk & Transport Museum at Cultra and operates with water-powered bellows. A third spade mill exists at Templepatrick, County Antrim, but this is driven by a water turbine. McMahon's is therefore a significant survivor of this distinctive industrial heritage, with particular archaeological interest arising from its two wheels and the apparent non-water-powered bellows system.