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giữa các cá nhân vàmỗi phân chia địa tầng của lớp đất đá Thời gian người Silurian Bohemia (Barrande 1852). Nhiều tác giả sau đó đã thông qua sự bao gồm thông tin tần số trong bảng xếp hạng phạm vi phân loại. Đến năm 1920, hình thức trình bày này đã thường xuyên được sử dụng để minh họa các kết quả hoặc l | 222 CATHY BARTON Fig- 3. Section of a colour-coded province map of the Mid-Atlantic Ridge in the equatorial Atlantic. The red yellow and green areas show highest elevation. Reproduced from a map worksheet in the Heezen Collection. Library of Congress photographer Gary North authors Bruce c. Heezen Marie Tharp Date 1960 . Fig. 4. The World Ocean Floor Panorama authors Bruce c. Heezen and Marie Tharp Date 1977 and copyright by Marie Tharp 1977. Reproduced by permission of Marie Tharp. 1 Washington Ave. South Nyack. NY 10960. MARIE THARP AND OCEAN FLOOR CARTOGRAPHY 223 sequential or genetic development of oceans from mid-ocean ridges. The Indian and Atlantic Oceans supposedly began as continental rifts and slowly grew and the rifts in East Africa the Red Sea and the Gulf of Aden were comparable features at different stages of development Heezen 1962 . Physiographic diagrams a reflection of changing scientific attitudes Many scientific disciplines not least geology frequently proceed by the use of visual thinking and aesthetic considerations rather than deductively through logic or inductively from empirical data Miller 1981 . This aesthetic method contributed significantly to the reintroduction of the notion of continental drift. The rifted MidAtlantic Ridge suggested that the Earth s crust had moved laterally and the diagrams contributed to the demise of geology s old permanence theory. But Heezen and Tharp did not propose that continental drift caused the rift. Rather the diagrams attracted the attention of other geoscientists who made an acceptable case for continental drift and later for plate tectonic theory which incorporated drift Le Grand 1988 . In 1958 Heezen acknowledged that palaeomagnetic studies and other new data implied lateral continental motion but he advocated expansionism not drift. Expansion had been proposed previously in the twentieth century.27 In 1960 Heezen and Tharp promoted expansion while Harry Hess 1906-1969 proposed what became after .