The Quarterly journal of the Geological Society of London . dbe originallv much weathered, as the thin ice would not have mucherosive action on the rocks below,2 and consequently the bouldersare not likelv to be striated. All this is in agreement with thefacts actually observed. 1 P. F. Kendall, in G. F. Wrights Man & the Glacial Period 1892. p. 166 jand G. W. Lamplugh, Geology of the Isle of Man Mem. Geol. Surv. 1903,pp. 393 & 394. - An interesting example illustrating this point may be cited from theeastern slopes of Black Hameldon. Undisturbed subsoil and more finely-divided material, appar
The Quarterly journal of the Geological Society of London . dbe originallv much weathered, as the thin ice would not have mucherosive action on the rocks below,2 and consequently the bouldersare not likelv to be striated. All this is in agreement with thefacts actually observed. 1 P. F. Kendall, in G. F. Wrights Man & the Glacial Period 1892. p. 166 jand G. W. Lamplugh, Geology of the Isle of Man Mem. Geol. Surv. 1903,pp. 393 & 394. - An interesting example illustrating this point may be cited from theeastern slopes of Black Hameldon. Undisturbed subsoil and more finely-divided material, apparently produced by ordinary weathering from the gritand shale upon which they rest, are covered by from 6 inches to a foot ofDrift with rounded stones (in one case with chert also). Here not only wasthe ice thin and near its extreme limit, but the soil and subsoil over whichit passed were probably frozen hard and so preserved intact. <352 to 53 53O Is •si5£ -Si 5£ 53 p w I *5 h < i-^ 1 «* *3 u \ ^ < \ » SS J m o o 2 D QWH< U< o. Yol. 70.] THE GLACIAL GEOLOGY OP EAST LANCASHIRE. 215 The Thickness of the Ice-Sheet. The extent of the Local Drift suggests that the upper layer ofclean ice was from 200 to 300 feet thick, whence we may infer thatthe actual surface of the ice-sheet at Winter Hill probahlyreached an altitude of 1750 feet above From the maximum altitudes attained by the North-WesternDrift, from Winter Hill to the Pennines, the surface of theice-sheet has been estimated to have fallen eastwards between4 and o feet in a mile. Hence, assuming this gradient to becontinued westwards to the middle of the Irish Sea, the altitudeof the surface of the ice-sheet would be there approximately2100 feet above present sea-level, in the latitude of Winter Hill,at the culmination of the Glacial Period. V. Systems of Glacial Drainage. Prof. Hull1 described several watersheds in this region asoccurring in vallevs, and called attention to the fact that thesevalleys
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