It is a pity that these alluvial deposits, which give such good evidence as to the order in which different peoples or different states of society succeeded one another on the earth, should be so valueless as a means of calculating the time of their duration; but one can easily see that they must always be so, by considering how the thickness of the deposits is altered by such accidents as the formation of a mud-bank, or the opening of a new channel,—things that must be continually occurring in districts where this very accumulation is going on. The only place where any calculation can be based upon its thickness is on the banks of the Nile, where its accumulations round the ancient monuments may perhaps give a criterion as to the time which has elapsed since man ceased to clear away the deposits of the river.2
As an instance of the tendency of alluvial deposits to entomb such monuments of former ages, I must mention the temple of Segeste, which stands on a gentle slope among the hills of northern Sicily. I had heard talk of the graceful proportions of this Doric temple, built by the Greek colonists; and great was my surprise, on first coming in sight of it, to see a pediment supported by two