Scientific Essays and Lectures

Excerpt: ...first hypotheses, are not always the right ones; and if he be a modest man, he will consider the fact that many thousands of thoughtful men in all ages, and many thousands still, would say, that the glen can only be a few thousand, or possibly a few hundred, years old. And he will feel bound to consider their opinion; as far as it is, like his own, drawn from facts, but no further. So he casts about for all other methods by which the glen may have been produced, to see if any one of them will account for it in a shorter time. 1. Was it made by an earthquake? No; for the strata on both sides are identical, at the same level, and in the same plane. 2. Or by a mighty current? If so, the flood must have run in at the upper end, before it ran out at the lower. But nothing has run in at the upper end. All round above are the undisturbed gravel-beds of the horizontal moor, without channel or depression. 3. Or by water draining off a vast flat as it was upheaved out of the sea? That is a likely guess. The valley at its upper end spreads out like the fingers of a hand, as the gullies in tide-muds do. But that hypothesis will not stand. There is no vast unbroken flat behind the glen. Right and left of it are other similar glens, parted from it by long narrow ridges: these also must be explained on the same hypothesis; but they cannot. For there could not have been surface-drainage to make them all, or a tenth of them. There are no other possible hypotheses; and so he must fall back on the original theory