Sheet  42sw, Old Series 1". 1873. First edition, late issue. Glamorganshire: Brecon Beacons, Dowlais in SE corner. Hand-coloured engraving, 45 x 61cm. Base map 1832, pre-railway, geology not dated although geologists named as typical for earliest geological maps, issued 1873.  Flat , clear plate mark, full margins, slightly age-toned, clean, colours bright. Minor marginal tears to side margins. Engraving skewed on sheet. Neatly drawn in by hand, the course of the River Taf Fawr and three then proposed reservoirs, which now exist.  Stencilled no in lower left corner. In good condition.