180 FRAGMENTS OF SCIENCE. 
which runs down to the very bottom of the principal one". 
The aspect of this smaller chasm f rom bottom to top proves to 
demonstration that water had in former ages been there at 
work. It is scooped, rounded, and polished, so as to render 
palpable to the most careless eye that it is a gorge of 
erosion. But it was regarding the sides of the great chasm 
that instruction was needed, and from its edge nothing 
to satisfy me could be seen. I therefore stripped and 
waded into the river until a point was reached which com- 
manded an excellent view of both sides of the gorge. The 
water was cutting cold, but I was repaid. Below me on 
the left-hand side was a jutting cliff which bore the thrust 
of the river and caused the Aar to swerve from its direct 
course. From top to bottom this cliff was polished, rounded 
und scooped. There was no room for doubt. The river 
which now runs so deeply down had once been above. It 
has been the delver of its own channel through the barrier 
of the Kirchet. 
But the broad view taken by the advocates of the frac- 
ture theory is, that the valleys themselves follow the tracks 
of primeval fissures produced by the upheaval of the land, 
the cracks across the barriers referred to being in reality 
portions of the great cracks which formed the valleys. 
Such an argument, however, would virtually concede the 
theory of erosion as applied to the valleys of the Alps. 
The narrow gorges, often not more than twenty or thirty 
feet across, sometimes even narrower, frequently occur at 
the bottom of broad valleys. Such fissures might enter 
into the list of accidents which gave direction to the real 
erosive agents which scooped the valley out; but the forma- 
tion of the valley, as it now exists, could no more be 
ascribed to such cracks than the motion of the railway 
train could be ascribed to the finger of the engineer which 
turns on the steam. 
These deep gorges occur, I believe, for the most part in 
limestone strata; and the effects which the merest driblet 
of water can produce on limestone are quite astonishing. 
It is not uncommon to meet chasms of considerable depth, 
produced by small streams the beds of which are dry fora 
large portion of the year. Eight and left of the larger 
gorges such secondary chasms are often found. The idea 
of time must, I think, be more and more included in our 
reasonings on these phenomena. Happily, the marks 
