George Mathewson, 1835; apse by C J Menart, 1921. Rectangular-plan aisleless cathedral with Gothic facade, basement halls and 4-storey, 5-bay presbytery adjoined to S gable. Pale sandstone ashlar facade, rubble sides with ashlar dressings, grey slate roof. Tall Tudor-arch traceried windows with hoodmoulds and mask label stops to front elevation; buttresses with crocketted finials to front elevation, coped
parapet with cross-finial to centre gable, crenellated and sloping
to sides, ashlar-coped skew to rear.
FRONT ELEVATION: 3-bay. 2-leaf doors to slightly advanced ground floor centre bay with vertically-astragalled fanlight, multiple-moulded pointed-arch doorpiece with nook shafts and crocketted ogival hoodmould rising through crenellated parapet, stepped 3-light window above; single window over paired canopied niches to flanking bays;
Tudor-arched door to left and right return bays.
SIDE ELEVATIONS: 5 margined nave windows over bipartites to basement.
INTERIOR: wide aisle-less nave; plastered timber roof on corbelled bosses; rear gallery on 4-centred arch arcade of clustered columns. Nook-shafted windows with some stained glass by William Wilson, 1957-71. Painted panels of SS Margaret, Catherine and George; Stations of the Cross. Gothic altars of the Sacred Heart and of Our Lady of Perpetual Succour. Timber traceried altar rail; marble pulpits. 4-pointed Sanctuary arch with nook shafts on angel corbels; coloured
marble and timber panelled apse, remodelled 1921; traceried High Altar with curved painted reredos.
PRESBYTERY: adjoining S gable of cathedral, pierced at 4th floor and roof level by the apse. 3-storey raised to 4-storey, 5-bay, centre bay recessed with fanlight over later projecting pedimented porch. Leaded glass tripartite over. Harled stair drum added 1921 rises through 1st and 2nd floors. Flat roof with railed parapet. Canted harled apse to roof with pointed arch windows and incised cross. Rubble-built gables with circa 1870 channelled ashlar porch added to E. Gable end stacks.
Timber 12-pane sash and case windows.
FORMER SEA WALL: forms boundary wall to S, originally the sea wall of the Town Hospital. 18th century; random rubble, ashlar entrance, later garage door to E.