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Much work has been done in the last decade toward setting up a worldwide stratigraphic scale based on zonal subdivisions. The outlook for resolving the remaining problems regarding such a worldwide scale is optimistic for the warm-water belt; however, the cold-water Arctic and Antarctic areas present greater difficulties. The erroneous assumption is commonly made that sections in cold-water basins can be dated on the basis of concomitance of definite species of certain genera in subtropical sections. Little is known about rates of evolution for particular groups in various regions. Disagreement exists on the necessity of working out independent zonal scales for Arctic regions. Such scales obviously have merit; however, it might be wise to use a local zonal scale for geologic maps, where a single scale is required, in conjunction with a system of indices indicating the degree of precision with which a certain division is isolated.

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