Geology. 157 



from unaltered peridotite to the chrysotile may be divided roughly 

 into four zones as follows : (1) unaltered peridotite ; (2) partial 

 serpentinization of the olivine, with pyroxene more or less unaf- 

 fected ; (3) olivine completely, and pyroxene partially, serpentin- 

 ized — this zone constitutes the massive serpentine "bands" ; (4) 

 complete serpentinization of both olivine and pyroxene — this zone 

 forms the chrysotile " veins." The serpentinization has proceeded 

 outward from joint planes, etc., through the agency of siliceous 

 solutions which, permeating the walls on either side of such fissures, 

 have first acted' on the olivine content of the rock and from the 

 resulting concentrated aqueous solutions of olivine, serpentine has 

 been deposited in the form of microscopic fibers. The expansion 

 attending this reaction tended to render the rock more porous and 

 permit the solutions to reach fresh zones of the rock and carry 

 the change further on. The result has been that in the zone 

 immediately bordering the fissures the serpentinization of the 

 rock has been complete, while beyond this there is a more or less 

 gradual transition until the unaffected peridotite is reached. The 

 structure of the rock has changed progressively with the serpen- 

 tinization. Even in the massive serpentine the structure of the 

 original rock can at times be seen, and where, further, more or less 

 unaltered pryoxene crystals yet remain and the magnetite is dis- 

 seminated much as it occurs in the original peridotite. It is only in 

 the chrysotile vein that the original structure is entirely lost, even 

 to the extent that most of the iron ore has here collected along- 

 certain definite zones. The chrysotile of the veins is believed to 

 be the result of the parallel position and transverse attitude 

 assumed at the very outset by the minute fibers, and of their sub- 

 sequent growth in only one direction. The ultimate length of 

 the fibers is limited only by the width attained by the completely 

 serpentinized zone. w. e. f. 



4. Contributions to the knowledge of RichtJiofenia in the 

 Permian of West Texas j' by Emil Bose. Bull. University of 

 Texas, 1916, No. 55, 52 pp., 3 pis., 1 text fig. — Along and detailed 

 description of the brachiopod genus Richthofenia and the two 

 Texas species R. permiana and R. uddeni. The author, after a 

 review of the geographic and geologic distribution of the species 

 of the genus, concludes that thej^ are characteristic of the Permian 

 and were especially common in the early middle Permian. 



c. s. 



5. Contributions to Geology; reprinted from the Johns Hop- 

 kins University Circular, March, 19 17, 129 pp., figs. — The first 

 paper in this set is by Professor W. B. Clark, who gives a short 

 history of the rise of geological surveys. E. B. Mathews treats 

 of '* The use of average analyses in defining igneous rocks," and 

 J. T. Singewald of " The role of mineralizers in ore segregations 

 in basic igneous rocks." F. Reeves writes on " The origin of the 

 natural brines of the oil fields." The other seven papers, by 

 Berry, Gardner, Woodring, Thom, Wade, and Dorsey, deal with 

 Mesozoic and Cenozoic stratigraphy and faunas. The pamphlet 

 is replete with new and important information. c. s. 



