GEOLOGY formations, and an occasional fragment of granite or volcanic grit. 1 Speaking generally the massed gravels are more abundant in the north than in the south, and more persistent towards the base of the sub- division than near its summit. They are largely quarried for road metal and gravel in Trentham Park, Cannock Chase, south of Cheadle, Longton, and in many localities bordering the South Staffordshire Coalfield. To the west of the South Staffordshire Coalfield the sub-division is situated with apparent perfect conformity between the Lower and Upper Mottled Sandstone, but elsewhere in the county rests with a great discord- ance on the various members of the Carboniferous rocks or on 'Permian.' This unconformity can nowhere be better illustrated than by the outliers at Endon and around Leek, where the nearly horizontal pebbly Bunter sandstones rest on highly inclined or sharply folded Lower Carboniferous rocks. In its course along the western margin of the South Staffordshire Coalfield the outcrop is indicated by conspicuous ridges, such as Abbots Castle Hill, near Trysull, and Kinver Edge. Along the eastern side of the coalfield the outcrop extends in a well marked ridge from near Birmingham northward to Aldridge. The greatest expanse however constitutes the open undulating heather-clad moorland of Cannock Chase on which the characteristic weathering into deep coombes with inter- mediate rounded lobes is admirably illustrated. The same character is clearly portrayed round the North Staffordshire Coalfield, where the sub-formation gives rise to the picturesque woodlands of Maer, Swyn- nerton Park, Trentham Park, Burnt Wood and Bishops Wood. Perhaps the most interesting outcrop occurs in the Churnet valley between Cheddleton and Leek, where a small patch about seven miles long has been preserved in a deep pre-Triassic hollow excavated in the Lower Carboniferous rocks which on all sides surround and overlook the much newer formation. The mode and place of origin of the sandstones and shingle beds have given rise to much controversy among geologists. They have been regarded as the products of powerful oceanic currents ; another opinion holds them to be of sub-aerial origin, brought together by large rivers liable to heavy floods, or else by tumultuous torrents the effect of cloudbursts. Some geologists consider the pebbles to be derived from the breaking up of the conglomerates of the Old Red Sandstone ; others again would derive them from Palaeozoic rocks of different ages in rapid course of destruction by the ordinary agents of denudation acting during the Bunter period. Again, the views as to the source of origin are widely divergent : some geologists maintain that the pebbles were derived from the older formations in the north of England and Scotland ; others look to their source from an old rocky ridge extending between the south- west of England and western France ; while others think it not improb- able that much of the material might have been obtained from the older 1 W. Molyneux, ' On the Gravel Beds of Trentham Park,' Trans. North Staff. Nat. Field Club (1886) ; Geol. Mag. iv. 173 (1867). 21
