The occurrence of two Archæan groups in Shropshire is now well known to geologists. The chain of hills which strikes to the south-west from Lilleshall, north-east of Wellington, to the region south of Church-Stretton, is mainly composed of bedded volcanic rocks; but gneissic and granitoid types have been recognized at the Ercal and at Primrose Hill, the elevations forming the opposite extremities of the Wrekin, and a small exposure was detected near Hope Bowdler, east of Church-Stretton. A second axis of the old rocks, ranging parallel to the Wrekin chain, consists of volcanic ejecta and highly indurated grits, which are probably to be referred to the younger of the two Archæan groups hitherto recognized in the county. The relations between the volcanic and the gneissic systems is clearly defined by the Charlton Hill (see map) conglomerate (a band in the volcanic series), which contains numerous well-rounded pebbles of rock precisely similar to the granitoid gneiss of Primrose Hill. This fact implies a considerable break between the two groups.