its west side—great sloping tables of rock suddenly ended by a wall of a different stratum—a sort of serrated edge all the way down the inclined plane; you could not miss seeing it, for it cuts the view like the teeth of a saw! Now if the water, instead of rising to the top and then trickling down the old channel, which is still noticeable, had once found a vent on one of those shelving planes it would gradually fill up the whole cavity formed by the two planes, unless in the meantime it found some natural escape. As we know, the mountain is covered in a number of places with a growth or formation of bog, and this water, once accumulating under the bog, would not only saturate it, but would raise it—being of less specific gravity than itself—till it actually floated. Given such a state of things as this, it would only require sufficient time for the bog to become soft and less cohesive than when it was more dry and compact, and you have a dangerous bog, something like the Carpet of Death that we spoke of this morning."
"So far I can quite understand," said I. "But if this be so, how can the bog shift as this one has undoubtedly done? It seems, so far, to be hedged with walls of rock. Surely these cannot move."
Sutherland smiled. "I see you do apprehend! Now we are at the second stage. Did you notice as we went across the hill side that there were distinct beds or banks of clay?"
"Certainly! do they come in?"
