174 PETROLOGICAL ABSTRACTS AND REVIEWS 



Benson, W. N. "The Origin of Serpentine, a Historical and Com- 

 parative Study," Amer. Jour. Sci., XL VI (1918), 693-731. 



The author agrees with the general opinion that chrysotile- or 

 antigorite-serpentine of large ultrabasic masses is derived from the altera- 

 tion of originally intrusive peridotite; the hydration, in some cases at 

 least, having been brought about by the agency of waters emanating from 

 the same magma as that which produced the peridotite. Whether a 

 peridotite which escaped hydration during the igneous epoch can subse- 

 quently be changed to serpentine by the action of deep circulating 

 epigene waters is regarded as less clear though thought not improbable. 

 The reviewer is glad to see followed here his own mode of indicating by 

 asterisks, in the bibliography, works not seen by the writer. 



Benson, W. N. "The Geology and Petrology of the Great Serpen- 

 tine Belt of New South Wales," Parts VI (Appendix) and VII. 

 Proc. Linnean Soc. New South Wales, XLII (1918), 693-700, 

 XLIII (1918), 320-94. Map I, pis. 10, figs. 5. 



The preceding papers of this series were reviewed in J our. Geol., XXV 

 (1917), 493-95. In the present papers the rocks of the Attunga and 

 Loomberah districts, and of a portion of the Goonoo Goonoo Estate 

 are described. Two analyses of dolerites are given and keratophyres, 

 dolerites, albite-dolerites, and granophyres are described rather com- 

 pletely, although much-to-be-desired model percentages are not given. 



Berek, M. and Jentzsch, F. "Ein kleiner lichtstarker Mono- 

 chromator, besonders fiir mikroskopische Beobachtungen," 

 Zeitschr. f. Instrumentenkunde, 1914, 47-51. Figs. 2. 



Describes a small monochromator for the production of mono- 

 chromatic light. The instrument is only half as large as a petrographic 

 microscope, and is so arranged that the whole spectrum may be made to 

 pass through the opening without adjusting the light source or the 

 microscope. The visible portion of the spectrum is normally 12 mm. 

 but the emergence slit may be adjusted to any width. The emerging 

 ray may be made parallel, convergent, or divergent by means of a lens 

 in a sliding tube. 



