Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/549

1869.] MACKINTOSH—LANCASHIRE AND CUMBERLAND DRIFTS. 425 liquely to the slope of the hill. This looked like an instance of glaciation by the grounding of floating ice during the Upper-Boulder-clay period. Between the base of the slope and Dunnerholme, though stones of granite &c., may be found, few sections of drift have been exposed, so as to reveal the distinction between Boulder-clay and postglacial or recent marine deposits.

i. Drift Capping of Dunnerholme.—Dunnerholme is surrounded on three sides by sea, and on one side by land which has evidently been sea at no very remote period. The limestone strata mainly dip S.W., but towards the western side S.E. It is cliffed all round. The highest part of this semi-island is about 70 feet above the sea. It is more or less covered with Upper Boulder-drift from 2 to 5 feet thick. The drift, a red loamy clay, is well charged with rounded and half-rounded stones, many of them much more rounded than those now washed by the sea at the foot of the cliff. The stones consist of slate, porphyry, &c., with a small percentage of granite. The drift rests on a smoothed, hollowed, and funnelled limestone- surface, as before remarked. It is difficult to explain the presence of drift in such a perched position without supposing that the plateau once graduated into the neighbouring ground, and that since the deposition of the drift the sea has encroached all round so as to leave a bounding line of cliff. But if so, the conclusion can scarcely be resisted that isolated drift- covered plateaux in inland and upland regions must have been circumdenuded by the sea.

On the road between Dunnerholme and Dalton granitic boulders are common. Upper Boulder-clay, with its usual accompaniment of brick-pits, undoubtedly runs along the shore of the Duddon estuary to Barrow; but in the central part of the Furness peninsula the drift (where it is not decided pinel or cleanly washed sand and gravel) is so tinged with red oxide of iron from the older haematitic deposits, and is so inconstant in its character, as to render the task of correlating it very difficult. It varies from angular detritus and red loam to red gravelly clay. On the watershed between Ulverstone and Barrow the furthest east specimen of granitic drift I could find was near the village of Stainton. But though granite in Furness may be regarded as an indication of Upper Boulder-clay, it does not follow that the upper-drift sea extended no farther eastwards, but merely that the ice-laden current from the mountain source of the granite had here its boundary. I have not seen the clay on the coast at Rampside, near the southern point of the Furness peninsula, but, from information received, have no doubt that it is of Upper-Boulder age. Neither have I seen the sand hills to the south-east of Barrow.

j. Upper Boulder-clay at Barrow.—At the Dalton-road brick-pit, Barrow, the Upper Boulder-clay appears in such fall force as to justify the epithet applied to it in the S.E. of England by Mr. Searles V. Wood, jun.,—"The Boulder-clay." As usual it is comparatively sandy, soft, or loose in the upper part, and more argillaceous or marly and solid lower down. Near the surface, it is here of a dun bluish-brown colour, the bluish tinge increasing downwards. Its