Summary The paper presents a revised and detailed correlation of Yoredale limestones, from the Jew Limestone to the Great Limestone, from the Alston area across Northumberland into southern Scotland. Stratigraphical and micro-palaeontological evidence suggests that the Scar Limestone of Alston is the lateral equivalent of the “Five-Yard” Limestone of Greenhead and consequently of the Eelwell Limestone of north-east Northumberland. Lower in the sequence the Jew Limestone appears to split northwards into the Oxford and Barrasford limestones of Northumberland. Apart from a narrow area of thicker strata on the southern margin of the Northumberland Trough, the higher Yoredale beds in the trough do not exceed greatly in thickness those of the Alston Block.

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SUMMARY The Northumberland Trough is dominated by numerous east-north-eastward trending Caledonoid faults. A recent geophysical survey has indicated the presence of another dislocation of similar trend, but this is related to the Whin Sill and its associated dykes and probably acted as an important feeder in the Roman Wall area. New boreholes in the Settlingstones-Newbrough area show the Whin Sill to be intruded at an horizon close below the Colwell (=Single Post) Limestone, and confirm the variability of the Brigantian sequence in this part of the Northumberland Trough. These new data have thrown doubt on the correlation suggested by Frost and Holliday (1980, p. 34) for the Settlingstones Mine area. The development of minor rhythms towards the top of each cyclothem in these Brigantian sediments is compared with those pre-Asbian sediments proved towards the base of the Stonehaugh Borehole. They are considered to have formed under similar conditions of deposition.

Summary The Lower Limestone Group in central Northumberland (i.e. the Redesdale Limestone and overlying strata up to the base of the Oxford Limestone) consists of about 270 metres of beds of Yoredale facies of the Lower Carboniferous. They are predominantly arenaceous but include up to ten limestones of thickness between 1.2 and 6 metres. The lower (D 1 ) limestones become thinner north-eastwards and do not extend more than a few kilometres east of Elsdon. The higher limestones are more persistent, contain an influx of new species with D 2 affinities and are recognizable over a wider area of Northumberland. The equivalent measures in north-east Northumberland are of abnormal facies and correlation is therefore difficult but the Dun, Woodend and Watchlaw limestones of the latter area are equated respectively with the Middle Penchford, Lower Wishaw and Upper Wishaw limestones of the Otterburn area. To the south-west in the Roman Wall and Brampton districts the Naworth Limestone is considered to be the lateral equivalent of the Redesdale Limestone. Because the base of the Lower Limestone Group has been taken at different horizons in different areas its value as a chronostratigraphical division is reduced but the term is retained as defining a useful lithostratigraphical unit.

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