361 
The vagueness referred to by Dr. Southall arises, I think, from this, that 
I assume as proved certain views in physical geography with which he does 
not agree, and, therefore, the figures on which he relies cannot be applied to 
the statement of observations as given by me. For instance, I hold that 
broad valleys are formed by the rivers winding from side to side along the 
flatter parts, but that a river never runs in a shallow stream evenly covering 
the whole of the bottom of a valley. Again, I never knew a river with a 
uniform fall along its whole length, and believe that a slope of much less 
than a foot per mile along the flatter parts, with a fall of 6 or 10 feet at the 
rapids, would cut back a valley, though there might be no denudation going 
on, except at the rapids. The general principle upon which I lay so much 
stress, that a river cuts back at the rapids, and that the denudation of valleys 
is chiefly due to that kind of action, has received ample illustration this 
year. I have known the rapids cut back in some of our Welsh rivers many 
yards in the recent heavy floods. Nor can I follow Dr. Southall in his 
explanation of the formation of loess and gravels. The loess, or brick-earth, 
may be seen after floods have spread over the lowlands ; as, for instance 
commonly in the rivers which run into the Humber, Wash, and Thames 
estuary, and is only the mud which has settled down from the flood- water 
when it has been allowed to stand and the sediment to settle. This is a 
well-known phenomenon, and is directed and turned to account in the 
process of warping. But the gravel requires water running at a high velocity 
to transport it, and cannot be spread at one and the same time over the 
whole valley. 
Mr. Whitley confines his remarks to the question whether the objects 
appealed to in evidence are really the work of man or not, and refers to a 
collection I made many years ago to illustrate the probability that man, first 
adopting common natural forms, then modifying these, had the fashion of 
his tools suggested by nature. Mr. Whitley objects to receive my evidence 
that a finished weapon is the work of man, because I have stated that I have 
found specimens which I thought were natural forms, but which had received 
a blow or two which made them more likely to be useful, and because I 
would not venture to say whether those blows were accidental or given 
designedly by man. If I see a stone chisel-dressed all over, and recognise it as 
the work of man, because I have seen man make such things, but have not 
known them produced by nature, and I see also a weathered fragment under 
a crag broken by frost and fall, and I say I have no doubt that it has been 
broken by natural causes, is my evidence about these of no value because 
I refuse to say whether another piece which I find by a road is altogether 
natural or roughly-hewn by man ? 
