i88i.] 
Miniature Physical Geography. 
639 
VII. The Cutting Downwards of Rivers. 
The best miniature examples I have seen of rivers eroding 
for themselves deep channels, by cutting their way down- 
wards, were near the Barton cliffs, in Hampshire. But 
almost anywhere one may notice this general deepening of 
channel giving rise to a valley or ravine. There was, how- 
ever a special interest in one example I saw at Barton, 
which induces me to mention it here. At the base of the 
cliffs was an eroded surface of Barton clay which was com- 
paratively tenacious. But the surface was not even, the 
hollows being filled up with a less tenacious mixture of mud 
and sand. Across the whole of this flowed a little fresh- 
water stream, which had cut its way 6 or 7 inches into the 
surface. And it was interesting to notice that where the 
clay was tenacious the valley sides were steep, almost 
precipitous ; where the stream passed over the mixture of 
clay and sand, the sides were sloping at a very gentle 
angle. This gentle angle could not, however, I think, have 
been produced by the stream alone, but must have been 
the result of either rainfall or the spray from the waves at 
high tide. 
Those who have seen anything of river action on a large 
scale will have noticed how marked an effeCt the hardness 
of the rocks has upon the form of a river valley. Where 
the rocks are soft the valley is very broad and open ; where 
the rocks are hard the valley assumes the character of a 
gorge. Of this the rivers which take their origin in the 
Weald, and flow through the South Downs, afford well- 
known examples. The Rhine gives us another illustration. 
And if we read the “ Geological Report of the American 
Survey of the Colorado of the West,” we find a description 
of the same thing : — “ Where we passed through the first of 
these ranges (the Purple Hills) it has nearly a N.W. and 
S.E. trend, and in the immediate vicinity of the river is 
composed of a gray massive granite, which, yielding some- 
what readily to the aCtion of the elements, has formed slopes 
receding from the river, giving the pass an outline strikingly 
in contrast with that of most of the canons cut in the por- 
phyrite rocks higher up ” (p. 21). One of these ravines, the 
great canon, as is well known, has nearly perpendicular 
walls, which are in one place more than a mile high. Never- 
theless the American geologists ascribe its formation entirely 
to the aCtion of running water. 
An instructive small scale example of a river thus cutting 
