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he report of a lecture on "Geological Measures of Time," by Professor Hughes, before the Royal Institution of London. Hughes was, like myself, a companion of Sir Charles Lyell in some of his journeys, though belonging to a younger generation of geologists, and is an accurate observer and reasoner. "Another method of estimating the lapse of time is founded upon the supposed rate at which rivers scoop out their channels. Although no very exact estimates have been attempted, still the immense quantity of work that has been done, as compared with the slow rate at which a river is now excavating that same part of the valley, is often appealed to as a proof of a great lapse of time. "The fact of such an enormous lapse of time is not questioned, but this part of the evidence is challenged. "The previous considerations of the rate of accumulation of silt on the low lands prepares us to inquire whether there is any waste at all along the alluvial plains. Several examples were given to show that the lowering of valleys was brought about by receding rapids and waterfalls; for instance, following up the Rhine, its terraces could often be traced back to where the waterfall was seen to produce at once almost all the difference of level between the river reaches above and below it. At Schaffhausen the river terrace below the hotel could be traced back and found to be continuous with the river margin above the fall. The wide plains occurring here and there, such as the Mayence basin, were due to the river being arrested by the hard rocks of the gorges below Bingen so long that it had time to wind from side to side through the soft rocks above the gorges. When waterfalls cut back to such basins or to lakes they would recede rapidly, tapping the waters of the lake, eating back the soft beds of the alluvial plains, and probably in both cases leaving terraces as evidence, not of upheavals or of convulsions, but of the arrival of a waterfall which had been gradually travelling up the valley. So when the Rhone cuts back from the falls at Belgarde we shall have terraces where now is the shore of Geneva; so also when the Falls of Schaffhausen, and ages afterward when the Falls of Laufenburg have tapped the Lake of Constance, there will be terraces marking its previous levels. And so we may explain the former greater extent of the Lake of Zurich, which stood higher and spread wider by Utznach and Wetzikon before it was tapped by the arri
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