ORBICULAR GABBRO-DIORITE FROM DAVIE COUNTY, 

 NORTH CAROLINA.^ 



GENERAL STATEMENT. 



Spheroidal or orbicular structures have been observed in granites 

 and diorites among plutonic rocks from many parts of the world, 

 and especially celebrated are some of these occurrences in North 

 America and Europe. The best-known of the European localities 

 are Fonni^ in Sardinia, Wirvik^ in Finland, Slatmossa^ in Sweden, 

 Riesengebirge^ in Silesia, Mallaghderg*' in County Donegal, Ireland, 

 and Corsica. In America the structure seems to have been less 

 often observed than in Europe, though a number of occurrences have 

 been described, mostly among granites, from widely separated 

 localities. These have been made known through the publications of 

 Edward Hitchcock,^ Hawes,^ Chroustschoff,^ von Rath,'° Zirkel," 

 Kemp,^^ F. D. Adams,'^ and Lawson,^^ which include the following 



1 Published by permission of the state geologist of North Carolina. 



2 G. VON Rath, Sitzungsberichte der Niederrheinischen Gesellschaft, Bonn, June, 

 1885, p. 201; F. FouQUE, Bulletins de la Societe mineralogique de France, Vol. X 

 (1887), p. 57. 



3 B. Frosterus, Tschermaks Mineralogische und petrographische Mittheilungen, 

 Vol. XIII (1898), p. 177; Bull. Com. Geol. Finland, 1896, No. 4. 



4 W. C. Br5gger, och H. Backstr5m, Geologiska Foreningen i Stockholm, For- 

 handlinger. Vol. IX (1887), p. 351; H. Backstrom, ibid., Vol. XVI (1894), p. 107; 

 N. D. HoLST, OCH F. EiCHSTADT, ibid., Vol. VII, p. 134. 



5 F. H. Hatch, Quarterly Journal 0} the Geological Society, Vol. XLIV (1888), 

 p. 548. 



6 G. Rose, Poggendorff's Annalen, Vol. LXI, p. 624. 



7 Geology of Vermont, Vol. II (1861), p. 564. 



8 Geology of New Hampshire, Vol. Ill (1878), Part 4, p. 203. 



9 Bulletins de la Soci'te mineralogique de France, Vol. VIII (1885), p. 137. 



1° Sitzungsberichte der Niederrheinischen Geschellschaft fiir Natiir- und Heilkunde, 

 December, i, 1884. 



11 Fortieth Parallel Survey, Vol. VI (1878), p. 54. 



12 Transactions of the New York Academy of Sciences, Vol. XIII (1903), pp. 140-43 

 Science, N. S., Vol. XVIII (1903), p. 503. 



13 Bulletin of the Geological Society of America, Vol. IX (1898), p. 163. 



14 A. C. Lawson, " The Orbicular Gabbro Diorite at Dehesa, San Diego county, 

 Cahfornia," The University of California Publications, Bulletin, Department of 



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