not go into the matter thoroughly, for that old wolf of mine was so manifestly impatient that I should get to his wild-goose chase for the lost treasure-chest, that the time and opportunity were wanting. However, I saw quite enough to convince me."
"Well, how do you account for the change? What is your theory regarding the existence of limestone?"
"Simply this, that a lake or reservoir on the top of a mountain means the existence of a spring or springs. Now springs in granite or hard slate do not wear away the substance of the rock in the same way as they do when they come through limestone. And moreover, the natures of the two rocks are quite different. There are fissures and cavities in the limestone which are wanting, or which are at any rate not so common or perpetually recurrent in the other rock. Now if it should be, as I surmise, that the reservoir was ever fed by a spring passing through a streak or bed of limestone, we shall probably find that in the progress of time the rock became worn and that the spring found a way in some other direction—either some natural passage through a gap or fissure already formed, or by a channel made for itself."
"And then?"
"And then the process is easily understandable. The spring naturally sent its waters where there was the least resistance, and they found their way out on some level lower than the top of the hill. You perhaps noticed the peculiar formation of the hill, specially on
