The upward and downward movements which any country has undergone, and the succession of such movements, can be determined with much accuracy; but geology alone can tell us nothing of lands which have entirely disappeared beneath the ocean.

Here physical geography and the distribution of animals and plants are of the greatest service.

By ascertaining the depth of the seas separating one country from another, we can form some judgment of the changes which are taking place.

If there are other evidences of subsidence, a shallow sea implies a former connexion of the adjacent lands; but if this evidence is wanting, or if there is reason to suspect a rising of the land, then the shallow sea may be the result of that rising, and may indicate that the two countries will be joined at some future time, but not that they have previously been so.

The nature of the animals and plants inhabiting these countries will, however, almost always enable us to determine this question.