It is the lower stones that one is most afraid of.

So long as these remain fixed, there is no fear of any general movement but, if they went, the whole mass might come down.

This passage is less than three feet wide, and the bamboos are twelve feet long; so that each would make four, the width of the passage.

I propose to drive them tightly in, and fix them firmly with wedges.

They must be put in so that they will actually touch the stones, so as to prevent their making the slightest downward movement.