GEOPHYSICAL LABORATORY. 139 



foreshadow a period of world overpopulation, which is an extension of the 

 regional overpopulation of past times. 



(487) Note on enstatite, hypersthene, and actinolite. H. S. Washington and H. E. Merwin. 



Am. Mineralogist, 8, 63-67. 1923. 



The optical characters and chemical analyses are given of enstatite from 

 Espedal, Norway; hypersthene from Nain, Labrador; and actinolite from 

 Krageroe, Norway. The materials studied were those used by L, H. Adams 

 and E. D. Williamson in their study of the compressibility of minerals and 

 rocks. (See No. 484.) 



(488) A survey of existing crystal structure data. Ralph W. G. Wyckoff. J. Frankhn 



Inst., 195, 183-210; 349-365; 531-552 (in 3 parts). 1923. 



The existing studies of crystal structure are briefly considered in the light 

 of the results of the theory of space-groups, and a summary given of the 

 results of those determinations which appear from this standpoint to be 

 probably correct. 



From this review examples are collected of the insufficiencies of the older 

 methods of study based upon a single diffraction method and not making 

 full use of both available crystallographic information and the results of 

 space-group theory. These illustrations are held to be numerous and striking 

 enough to make indisputably clear the practical necessity of using the more 

 generally applicable methods of investigation now available. 



(489) The isomorphism of albite and anorthite. F. Zambonini. (Abstract by H. S. 



Washington.) Am. Mineralogist, 8, 81-85. 1923. 



This is an abstract of a paper by Zambonini (Rend. Accad. Lincei, 31, 295. 

 1922), in which he suggests that the isomorphism of the feldspars is to be 

 explained by the similar diameters of the mutually replacing atoms, especially 

 silicon and aluminum, sodium and calcium, and potassium and barium. He 

 holds also that equality in the sums of the valencies of the replacing elements 

 is essential. His views are compared with the similar suggestion of E. T. 

 Wherry, who, however, minimizes the importance of equality of the valencies. 



(490) On structure and isomorphism in crystals. Ralph W. G. Wyckoff. Am. Mineralo- 



gist, 8, 85-92. 1923. 



This paper is primarily a discussion from the standpoint of crystal analysis 

 of a recently proposed hypothesis which considers isomorphous replacea- 

 bility to be essentially conditioned by identity in size of the replacing and 

 replaced atoms. It is pointed out that neither do the atoms in crystals 

 have constant radii nor are crystals closely packed atomic groupings. The 

 connection between isomorphism in crystals and their atomic arrangements is 

 briefly discussed and the absence of a cause-and-effect relation between the 

 two indicated. Further, explanations of isomorphous replacements in terms 

 of ''atomic radii" are expressions in other words of the well-known rule of 

 similar molecular volumes. Taking as illustrative the case of the isomorphous 

 mixing of albite and anorthite, some of the conditions which must be fulfilled 

 in such a dual replacement are outlined, but it is emphasized that too little 

 is now known to permit the offering of a satisfactory explanation of even this 

 relatively simple instance. 



(491) Petrology of the Hawaiian Islands: I. Kohala and Mauna Kea, Hawaii. Henry S. 



Washington. Am. J. Sci., 5, 465-502. 1923. 



This paper is the first of a projected series of seven which will deal with 

 the petrology of the Hawaiian Islands. The studies are based on the largest 

 collection of Hawaiian rocks that has yet been available; some of them were 

 collected by the author, and many others by other geologists. Especial 



