A REPLACEMENT OF WOOD BY DOLOMITE 357 



usually obliterates the cell structure of the wood. An interesting 

 case in which the wood tissue is well preserved by calcite has recently 

 been described by C. W. Greenland/ Fragments of wood and 

 plant remains petrified by pyrite, and marcasite are recorded from 

 carbonaceous formations of many districts. Blum describes 

 replacements of wood by barite, from the Lias chalji beds of central 

 Germany; by cinnabar, from Bavaria; by fiuorite, from Saxony; 

 by sulphur, from Italy; and by malachite and azurite, from the 

 Urals and West Africa. The same author also records replace- 

 ments of wood or plant remains by gypsum, phosphorite,^ hematite, 

 limonite, siderite, sphalerite, galena, chalcopyrite, and chalcocite. 

 He mentions a case in which wood tissue is well preserved by 

 a kaolin-like substance most closely resembling halloysite. Blum 

 also discusses replacements of wood, from near Moutiers in the 

 French Alps, by a mineral closely resembling talc, and compares 

 this mineral with some pyrophyllite from the Thuringen district 

 in Germany. The pyrophyllite, however, is not described as 

 replacing wood. Grabau^ mentions chlorite as replacing plant 

 remains. 



In an article on the " Red Bed " type of copper ores, Rogers'' lists 

 as occurring in petrified wood: hematite, pyrite, bornite, chalco- 

 cite, chalcopyrite, covellite, melaconite, limonite, malachite, 

 azurite, and quartz. Of these, only hematite and pyrite are 

 considered as directly replacing wood. 



The dolomitized wood herein described belongs to the mineral 

 collections of Professor A. F. Rogers, of Stanford University, to 

 whom I am indebted for the privilege of describing it as well as 

 for suggestions as to the description itself. The specimen was found 

 in 1916 in the Midway Oil Field, Kern County, California, by 

 C. R. Swartz. It comes from what is locally known as the McKit- 

 trick formation, which may include sediments of upper Miocene, 

 Pliocene, and Pleistocene age.^ 



' C. W. Greenland, Econ. GeoL, Vol. XIII, pp. 116-19. 



^ Probably impure coUophane. 



3 A. W. Grabau, Principles of Stratigraphy. A. G. Seller & Co., 1913. 



1 A. F. Rogers, Econ. Geol., Vol. XI, pp. 366-80. 



5 Arnold and Johnson, U.S.G.S. Bull. 406. 



