In this address emphasis will be placed not on the utilization of the remains of marine organisms in solving problems of stratigraphic correlation, but on the value of the knowledge of them in attempts to reconstruct the physical and chemical conditions prevalent in the seas of the past. The area of the oceans of today constitutes about 70 per cent of that of the surface of the earth. Inspection of geological maps of large areas, such as those of continents, reveals that approximately 70 per cent of the land surface of the earth is formed by rocks of marine origin. Deposits of marine origin of Recent and ancient ages form about 90 per cent of the surface of the lithosphere. In comparison with the length of the radius of the earth, the thickness of the marine sediments is slight, at most only a relatively few miles, but these rocks. . .