176 CARNEGIE INSTITUTION OF WASHINGTON. 



(30) The crystal structure of some carbonates of the calcite group. Ralph W. G. Wyckoff. 



Am. J. Sci., 50, 317-360 (1920). 



By the same general method that has been employed in studying caesium 

 dichloriodide and sodium nitrate, a unique solution has been obtained for the 

 crystal structures of calcite and rhodochrosite. Of the assumptions commonly 

 made in crystal-structure study, the only one required in this determination 

 was that the atoms reflect X-rays in an amount roughly proportional to 

 their atomic numbers. The structure of siderite was shown to be so nearly 

 the same as that of rhodochrosite as to be indistinguishable by the means at 

 hand. Magnesite was also found to give the same sort of pattern and hence 

 to have the same general arrangement of atoms as the other members of the 

 group. 



The positions of the oxygen atoms, as determined by the present method and 

 by the spectrometer results, are compared. In this particular case, the "nor- 

 mal" dechne of intensities is in surprising agreement with the reflections. 

 Evidence is obtained from these crystal structures to show the existence of 

 groups of atoms, as carbonate groups, in the crystal. It is also pointed out 

 that unless every atom in the crystal is electrostatically charged, the outside 

 electrons of the atoms making up these crystals can not be arranged at the cor- 

 ners of cubes. 



Some connections are pointed out between the development of faces on cal- 

 cite and its crystal structure, and a way is indicated of deciding the most prob- 

 able indices of a plane when they are in doubt. The bearing of these structures 

 upon the question of what constitutes a series of isomorphous substances is 

 mentioned. 



A criterion is suggested for determining in the case of an hexagonal crystal, 

 whether the fundamental unit in a rhombohedron or an hexagonal prism. 



The use of gnomonic projection in studying Laue photographs'is mentioned 

 and a ruler is described, the use of which reduces the time and labor of making 

 such projections. The effect of the voltage impressed on the X-ray tube upon 

 the character of the Laue photograph is considered and the best conditions 

 for operating a tungsten tube for this work are stated. 



(31) The Katmai region, Alaska, and the great eruption of 1912. Clarence N. Fenner. 



J. Geol., 28, 28, 569-600 (1920). 



A preliminary account has been presented in this paper of observations made 

 by the writer as geologist of the expedition sent in 1919 by the National Geo- 

 graphic Society, in cooperation with the Geophysical Laboratory, to the Kat- 

 mai region. As a result of this work, evidence has been found that affords a 

 basis for extending considerably our ideas respecting the processes at work 

 during the eruption. 



It has been found that the volcanoes of this region, which form a continua- 

 tion of the Aleutian loop or festoon, are situated in an area of sedimentary 

 rocks remarkable for the absence of folding or obvious faulting. The more 

 recent lavas are basic andesites, contrasting greatly in composition with the 

 highly siUceous rhyolite of the last eruption. 



In the area of the Valley of Ten Thousand Smokes it is believed that the 

 injection of a sill or closely similar body of magma into the underlying strata 

 at the beginning of the eruption caused shattering of the rocks above it, and 

 these openings permitted the ascent of magma. The extrusion and inflation 

 of this magma gave rise to a great ash-flow or sand-flow, analogous in many 

 respects to the nuees ardentes of Pel^e and La Soufriei-c, and led to the forma- 

 tion of the parasitic cone of Novarupta. The fumaroles are thought to be 

 due to the continued evolution of volatile constituents from this body of 



