Tradition is no doubt often entirely erroneous; but it ought not, I think, to be summarily dismissed without at least critical examination. There are doubtless instances where it might come in to corroborate conclusions deducible from other and usually more reliable kinds of evidence. (4) But of all the sources of information regarding bygone mutations of the surface of the land, undoubtedly the most important is that supplied by the testimony of geology. Early human chronicles are not only imperfect, but may be erroneous. The chronicle, however, which Nature has compiled of her past vicissitudes, though it may be fragmentary, is, at least, accurate. In interpreting it the geologist is liable, indeed, to make mistakes; but these can be corrected by subsequent investigation, while the natural chronicle itself remains unaffected by them. Moreover, it embraces a vast period of time. Historical evidence in this country is comprised within the limits of nineteen centuries. The testimony from Celtic topographical names may possibly go back some hundreds of years further. But the geological record of the human period carries us enormously beyond these dates. Hence, in so vast a lapse of time, scope has been afforded for a whole series of important geological revolutions. On every side of us we may see manifest proofs of these changes. The general aspect of the country has been altered, not once only, but many times. The agencies that brought about these changes have, in not a few instances, preserved tolerably complete memorials of them. We are thus enabled to trace the history of lakes and rivers, of forests and mosses: we can follow the succession of animals that have wandered over the land, and many of which had died out ere the days of history began: we can dimly perceive the conditions of life amidst the earliest human population of the country: we can recover abundant evidence of the extraordinary vicissitudes of climate which, since these ancient times, have affected not this land only, but the whole northern hemisphere.