A curious thing followed.

At first it shot straight downward for a hundred feet, when it impinged against a projecting point of the mountain wall, knocked the fragments in every direction, as if it were a ball fired from a thousand-pounder, and bounded against the opposite side, further down, scattering fragments again.

By this time it had achieved an almost inconceivable momentum, and was shooting downward at a terrific rate.
In the depths of this narrow canyon, where the sunlight never penetrated for more than a few minutes at a time, it was always twilight.

At the bottom it was almost dark, so that the stream would hardly have been visible but for its yeasty foam.

At some point near the base, when the flinty stone was speeding forward like a meteor, it abraded a harder portion than before.