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Nature volume 49, pages 214215 | Download Citation

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American journal of Science, December.—An apparent time-break between the eocene and Chattahoochee miocene in southwestern Georgia, by Raphael Pumpelly. The Red Clay Hill region, a plateau extending through the south-western part of Georgia and adjacent northern Florida, has a maximum altitude of 300 feet, is sharply limited on the north by a declivity facing the eocene flat-land country, and consists of miocence deposits resting on eocene, both of which dip about 13 feet per mile to the south. The base of the plateau is formed by the white calcareous beds of the Chattahoochee group. A time-break between the latter and the eocene is evidenced by the almost general presence of a limestone conglomerate at the base of the Chattahoochee, immediately overlying eocene fossils, and the irregularity of the surface of demarcation. It seems possible that during miocene time the present plateau of southern Georgia was outlined by submerged islands of the eocene limestone. The Gulf Stream, after the creation of the central American barrier, found its way back to the Atlantic sweeping over southern Georgia and northern Florida, and supplying the food needed to build up the great organic beds of the Chattahoochee and Chipola. The lower flat-land country of central Georgia may represent the contemporaneous course of the cold current carrying less pure water and less nutriment.—The rise of the mammalia in North America, by H. F. Osborn. This second part deals with ancient and modern placental differentiation, the succession of the perissodactyls and the artiodactyls, a discussion of the factors of evolution, and a diagram illustrating the supposed descent of the mammalia from their Jurassic prototypes.—On the thoracic legs of Triarthrus, by C. E. Beecher. Some very perfect specimens of Triarthrus Becki, Green, in which nearly the entire calcareous and chitinous portions are represented by a thin film of iron pyrites, show, besides the antennæ already noticed, a complete series of thoracic legs becoming shorter towards the pygridium, but without any essential differences amongst each other. Each limb consists of two nearly equal members, one of which was evidently used for crawling, and the other for swimming. These two members and their joints may be correlated with certain typical forms of Crustacean legs among the Schizopoda, Cumacea, and Decapoda, and may be described in the same terms.—On the diamond in the Canon Diablo meteoric iron and on the hardness of carborundum, by George F. Kunz and Oliver W. Huntingdon. The carborundum made by Mr. Acheson, of Pittsburg, is capable of scratching most varieties of corundum, but not the diamond.

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https://doi.org/10.1038/049214a0

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