which the Rhymney Valley Water Board was to be a constituent member. Both Bills were passed in 1921 and in 1928 the Taf Fechan reservoir, having a capacity of 3,400 million gallons, was completed and became the main source of the water supply of the district.

THE RECORDING OF FOCHRIW ON VARIOUS

ORDNANCE SURVEY MAPS

The triangulation for south Wales was undertaken between 1800 and 1809 under the direction of Lieutenant - Colonel William Mudge and Captain Thomas Colby when the triangulation exercise was carried out by determining heights and distances by fixing the position of key trigonometrical stations within the area. The third volume of the Account of the Trigonometrical Survey, published in 1811, contains a full record of the work.

The first field survey commenced in 1811 and was probably competed by 1815. In 1820 it was first diagnosed that this early mapping was often inaccurate in comparison with the current work of field surveyors, and a systematic revision was undertaken in 1825 which intermittently progressed until 1831.

OS sheet 36, which covered the greater part of Glamorganshire and a small section of the eastern boundary with Monmouthshire, was published on 1 January 1833. Additional information regarding details of the rapidly expanding coal-field was added during the mid 1840's and railways added during the 1850 to July 1883 period. However, at this stage, without the benefit of sight of all the chronological versions of sheet 36 (later renumbered as sheet 67 Cardiff), determination of the actual progressive development of the area is not possible.

Sheet 36, which relates to the greater part of the County of Glamorgan, and part of its eastern border with the County of Monmouthshire, was first published on 1 January 1833. Additional geological information was added during the mid-1840's with numerous amendments being made in succeeding years due to the rapid expansion of the coal industry and related infrastructure.

From sheet 67 (Cardiff) dated 1882, being the successor to sheet 36, the village of Fochriw is non-existent, however, the railway lines and stations were added to this print in 1883, the topographical data of which was probably that as of the early 1830's.

The area between Fochriw and Pentwyn is labelled as Llwynau Iago or Dan y Ffocrhiw, and what may be Ffynnonau Duon, identifying the area around Pentwyn. Could these be the derivations of Llwyn Iago and Ffynnon Duon farms?