The petrography, sedimentation and provenance of the Wenlock rocks near Hawick, Roxburghshire

A petrographical description of the sediments is given, with particular reference to stratigraphical variation and provenance. It is concluded that the material was derived from a land-mass consisting largely of Ordovician spilites, cherts, acid lavas and sediments; together with metamorphic rocks, probably Dalradian, arkoses and granitic intrusions. The provenance conclusions are supported by the directional current structures, which indicate a predominantly north-westerly derivation for these rocks. The lithology of the greywackes and interbedded sediments is consistent with their deposition by turbidity currents, about which some new details are deduced. Furthermore, the evidence of current directions and variations in lithology suggest that the two Wenlock facies represent deposition on a “submarine-delta” (Hawick Group) and in fan accumulations in deeper water, at the mouths of submarine canyons (Riccarton Group). The area of Wenlock deposition is believed to have been separated by the Ordovician/Dalradian land-mass from a contemporaneous trough at Lesmahagow; but to have been in communication with the area of deposition in the Lake District.