180 FRAGMENTS OF SCIENCE. 



which runs down to the very bottom of the principal one. 

 The aspect of this smaller chasm from 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 

 and 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 hy 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. Right 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 



