THE AGE OF THE WYE. 
187 
awaj by a marine current, the water surface of which must 
have been several hundred feet above. For, from my observa- 
tions, I have found that the “ surface softening” before alluded 
to does not take place at anything like the same rate when the 
rock is always under water that it does when the rock is exposed 
to the air. In the places where the railway crosses the river, 
and where we founded the piers of the bridges on the rock 
bottom, as at Backney for example, the rock, though less than 
four feet below the ordinary surface of the water, was still 
hard and but little softened. 
Returning again to the consideration of the course of the 
river. It may be noticed, by a glance at the ordnance map, 
that, all along its course for many miles, the river runs across 
its alluvial lands in “ bends ” of its own peculiar form, and of 
about the same average length. The average length of one of 
these bends, in the six miles under consideration, is about 1690 
yards from the point where its w’aters fret the marginal cliff, to 
that where it next returns to the same cliff. 
These bends are constantly descending the course of the 
river, as might be expected from the fact that the alluvial land 
is on an incline of feet in a mile, and as may be proved by an 
inspection of any one of the bends on the wall map. Take, for 
instance, the “ bend ” between the Sheepwash and Ross. The 
banks marked with the dark lines are those which are being 
washed away, while those with the faint lines are advancing, 
^sow, if we imagine that all the dark banks lose a yard, while the 
same breadth is gained on the faint line banks, the whole 
“ bend ” will, evidently, have descended a yard southwards 
through the alluvium. This process is always going on when 
the water is high, and, in an average of years, the river channel 
progresses downwards at a rate which I shall now endeavour to 
ascertain. 
