Brief Notices. 285 



published in a large paper by Everding in 1907 becomes available in 

 English for the first time. 



4. The Banket. By Robert B. Young. Gurney & Jackson, 1917. 



8s. 6^. net. 

 A S the formation, or rather the series of formations, responsible 

 XX for the world's greatest goldfield, the banket of the Rand has 

 naturally received much attention from geologists as well as from 

 the miner, whose interest is purely economic. Professor Young's 

 book is essentially a petrographic account of the banket and of the 

 associated rocks, concluding with a discussion of the origin of the 

 gold. Allogenic (including pebbles and matrix) and authigenic 

 constituents are separately dealt with, gold being regarded as primarily 

 a member of the former, though afterwards subject to solution and 

 reprecipitation. A noteworthy feature of the book is the profusion 

 and beauty of the plates with which it is illustrated. 



5. Correlation and Chronology in Geology on the Basis of 

 Pal^ogeography. By C. Schuchert. Bull. Geol. Soc. Am., 

 vol. xxvii, p. 491, 1916. 



LIT the first section of the paper the rise of geological chronology 

 is described, and present views regarding the permanency of 

 continents and oceans, and the bearing of diastrophism on chronology, 

 are discussed. It is stated that crustal unrest is recorded in North 

 America by at least fourteen epochs of mountain-making. Of these 

 eight are " disturbances" of lesser import, while six are " revolutions " 

 belonging to the more critical periods of the earth's history. The 

 methods in use for the determination of stratigraphical sequence and 

 correlation form the subject of the second section, and those dealt 

 with are the sedimentary, the palseontological, thepalaeogeographical, 

 and the diastrophic methods. The third section is devoted to the 

 palaeogeography of western North America during the Mesozoic Era, 

 and nine maps illustrating the general conclusions are given. 



6. On Synantetic Minerals and Related Phenomena. By J. J. 

 Sederholm. Bull. Comm. Geol. Einlande, No. 48, 1916. 



BY the term synantetic, Sederholm proposes to designate those 

 minerals that occur only where two definite minerals would 

 otherwise meet. Such are the reaction rims, kelyphitic borders, and 

 coronas occurring between various femic and salic minerals in basic 

 rocks, and the intergrowth of plagioclase and vermicular quartz 

 (to which the author gave the name myrmekite some years ago) that 

 occurs in acid rocks between the boundaries of potash and soda-lime 

 felspars. With regard to the former, which are described in great 

 detail and with very full abstracts of the literature, Sederholm comes 

 to the conclusion that they are referable to metamorphic processes. 

 In the case of myrmekite and other analogous structures, the 

 literature is again quoted at great length and a large number of 

 new observations are placed on record. The various theories are 



