552 SCIENCE PROGRESS 



Inclusions of epidosite, chlorite-rock, hornblende-schist, 

 and biotite-felspar-schist, within amphibolite, are described as 

 due to a migration and segregation of material during meta- 

 morphism, a process which is called metamorphic differentiation. 

 Rocks identical with the charnockite series of India were found, 

 and are believed to represent a suite of igneous rocks that 

 have suffered complete recrystallisation under the conditions 

 of Grubenmann's kata zone of metamorphism. 



W. Lindgren discusses volume changes in metamorphism 

 (Journ. GeoL 191 8, 26, 542-54), and upholds the view pre- 

 viously advanced by him in relation to metasomatism in mineral 

 deposits, that metamorphism by replacement does not nor- 

 mally involve changes of volume. 1 he volume of replacing 

 mineral equals the volume of mineral replaced, the substitu- 

 tion taking place particle by particle, not molecule by molecule. 

 This view is based on the geological evidence that little or no 

 change of volume has occurred in rocks that have undergone 

 metamorphism, and on the frequent preservation of texture 

 and structure in the altered rocks. 



A. F. Rogers illustrates an occurrence of a core of periclase 

 within brucite in a crystalline limestone from California (Amer. 

 Journ. Sci. 191 8, 46, 581-6), and shows that the hydration 

 of periclase to form brucite has probably been accomplished by 

 ascending hydrothermal solutions. At a later stage the 

 brucite has often been converted to hydromagnesite. 



Origin of Sedimentary Rocks. — A. N. Winchell and E. R. 

 Miller publish an account of a remarkable dust-fall that took 

 place over Wisconsin and Michigan on March 9, 191 8, illus- 

 trating the importance of wind as a geological agent (Amer. 

 Journ. Sci. 191 8, 46, 599-609). The evidence presented 

 shows that a single storm transported over a million tons of 

 rock a thousand miles or more. From the nature of the 

 material it is believed to have been derived from an arid region 

 to the south-west (Arizona or New Mexico), where siliceous 

 felspathic rocks are abundant. 



The loess of Louisiana is shown by F. V. Emerson to be of 

 aeolian origin (Journ. Geol. 191 8, 26, 532-41). From the evi- 

 dence of amount, thickness, and chemical composition of 

 the material it is inferred that the principal depositing winds 

 were southerly and westerly. 



The bulky volume recently issued by the Carnegie Insti- 



