ABSTRACTS 



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GEOCHEMISTRY.—rAe composition of crinoid skeletons. F, W. 

 Clarke and W. C. Wheeler. U. S. Geological Survey Profes- 

 sional Paper 90-D. Pp. 5. 1914. 



This investigation relates to the formation of marine sediments and, 

 therefore, of sedimentary rocks. A single group of existing organisms 

 was studied, namely the crinoids, and their contribution to the sedi- 

 ments was established. The material was furnished by Mr. Austin H. 

 Clark, of the U. S. National Museum, and consisted of 24 specimens rep- 

 resenting 21 distinct genera, with a range of habitat from northern Japan 

 to the shores of the Antarctic Continent. All of the crinoid skeletons 

 consisted of calcium and magnesium carbonates, with minor impurities, 

 and the proportion of MgCOs ranged from 7.28 to 12.69 per cent. The 

 crinoids, therefore, contribute notable quantities of magnesia to the 

 marine sediments. The proportion of magnesia, however, varied re- 

 markably with temperature. The crinoids from high latitudes ran lowest 

 in MgCOs; those from warm regions ran highest; the variation being 

 curiously regular. So far as the authors are aware, a regularity of 

 this order, which they do not attempt to explain, has never been 

 observed before. 



Ten fossil crinoids, ranging from the Ordovician to the Eocene were 

 also analyzed. These showed no regularities whatever, for they had 

 evidently been much altered by leaching, and by the infiltration of 

 foreign material. F. W. C. 



GEOLOGY. — Reconnaissance of the Grandfield district, Oklahoma. M. J. 



MuNN. U. S. Geological Survey Bulletin 547. Pp. 83, with maps, 



views and sections. 1914. 



The Grandfield district embraces about 360 square miles in southern 



Oklahoma, including the southeastern part of Tillman County and the 



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