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