As to the free use of the sea, Selden admits that to prohibit innocent navigation would be contrary to the dictates of humanity;[668] but he held that the permitting of such innocent navigation does not derogate from the dominion of the sea--it is comparable to the free passage on a road across another’s land--and it cannot always be claimed as a right. With respect to the argument that the sea cannot be appropriated because of its physical properties, he points to the example of rivers and springs, which even by Roman law may be appropriated, as well as of lakes. It is not true that the sea has no banks or limits: it is clearly bounded by the shores; some seas, as the Caspian, are completely enclosed, and the Mediterranean is so everywhere except at the Straits of Gibraltar. Elsewhere there are islands, rocks, promontories, by which boundaries may be determined; and limits may be set in the open sea by nautical science, as in the fixing of latitude and longitude; and that was shown by the Bull of Pope Alexander VI., and the hundred-mile limit of the Italians. Selden denies that the sea is inexhaustible from promiscuous use. On the contrary he says a sea may be made worse for him that owns it by reason of other men’s fishing, navigation, and commerce, and less profit accrue from it, as where pearls, corals, and other things of that kind are produced. In such cases the abundance may be diminished by promiscuous use just as readily as in the case of metals and suchlike on land; and the same argument applies to all kinds of fishing.[669]