It is running strong--but it is not deep, and there is just room to walk.

Make haste, Curdie.' He tried, but the hole was too small for him to get in.
'Go on a little bit he said, shouldering his pickaxe.

In a few moments he had cleared a larger opening and followed her.

They went on, down and down with the running water, Curdie getting more and more afraid it was leading them to some terrible gulf in the heart of the mountain.
In one or two places he had to break away the rock to make room before even Irene could get through--at least without hurting herself.

But at length they spied a glimmer of light, and in a minute more they were almost blinded by the full sunlight, into which they emerged.