gallan and raddia , although the whiteness of their faces and the transparence of their eyes did not betray it , were in fact terrified by the immensity of the sea , and by the prospect of not only crossing it by air but actually landing on an island in its midst an island , furthermore , that rose and sank entirely unpredictably , and which would take them ( if not to the bottom of the sea ) to an even less familiar place at the other end of the world .