Nearly a century ago one school of Geology taught that every part of the land has once been beneath the sea, and every part of the oceans has once been land (Lyell). The theory of another school was: once a continent, always a continent; and its natural corollary: once an oceanic basin, always an oceanic basin (Dana). Later came an intermediate school which held that no proof exists that individual continents have always remained the same, and that parts of the ocean or even of the dry land may tomorrow sink to form new depths (Suess). The teaching of the first-mentioned school has gone out of fashion, but the other two have much in common, one being strictly conservative and the other liberal in its interpretation of the permanency in the earth’s grander features. The writer belongs in the last-named school, holding that both continents and oceanic basins are, . . .