420 JOURNAL OF The; Washington academy of sciences vol. 11, no. 17 



GEOCHEMIvSTRY.— T/ze chemistry of ike Earth's crust. Henry S. Wash- 

 ington. Journ. Franklin Inst. 190: 757-815. 1920. 



The number of essential rock-forming minerals is very small. They are 

 mostly silicates of Al, Fe, Mg, Ca, Na, and K. Any two or more of these 

 minerals (with two exceptions) may occur together and in all proportions. 

 The chemical characters of igneous rocks are summarized in the paper and 

 the ranges and maxima of the various constituents are given. The average 

 igneous rock is considered and, after some discussion of the sources of error in- 

 volved in the calculation, a new average (based on 5179 analyses) is given. 

 The average rock is shown to be approximately a granodiorite. The average 

 composition of the Earth's crust in terms of elements is also given. Twelve 

 elements (O, vSi, Al, Fe, Ca, Na, K, Mg, Ti, H, P, and Mn) make up 99. Gl 

 per cent of the crust. 



The elements are referred to two main groups in the periodic table: (1) 

 the petrogenic elements, characteristic of and most abundant in igneous 

 rocks, of low atomic weight and occurring normally as oxides, silicates, 

 chlorides, and fluorides; (2) the metallogenic elements, rare or absent in ig- 

 neous rocks, but occurring as ores, of high atomic weight, and forming in 

 nature metals, sulfides, arsenides, etc., but not oxides or silicates. The 

 suggestion is made that beneath the silicate crust of petrogenic elements 

 is a zone essentially of nickel-iron, and beneath this a central core of the 

 metallogenic elements. This vertical distribution is in accord with Abbot's 

 views as to the distribution of the elements in the Sun. 



In igneous rocks and minerals the elements show a correlation, in that 

 certain of them are prone to occur with others, and a similar limited correlation 

 is apparently true of the animal and vegetable kingdom. 



The idea of "comagmatic regions," that is, the distribution of igneous 

 rocks in regions of chemically related magmas, is discussed, and some of these 

 are briefly described. 



The calculation of rock densities from their chemical composition is dis- 

 cussed, and the average chemical compositions and densities of the conti- 

 nental masses and oceanic floors are given. It is shown by these that the 

 average densities of the continents, ocean floors, and various smaller regions 

 of the earth stand in inverse relation to their elevations. The bearing of this 

 relation of average density and elevation on the theory of isostasy is pointed 

 out, and it is shown that the data presented are confirmative of the theory. 



H. S. W. 

 VOLCANOIvOGY.— Two gas collections from Mauna Loa. E. S. Shepherd. 

 Bull. Hawaiian Volcano (3bs. 8: 65-67. 1920. 



Through the courtesy of Dr. T. A. Jaggar, Jr., of the Hawaiian Volcano 

 Observatory, two tubes of gas were received which he collected in November 

 1919 from the flow on Mauna Loa. These are the first gases collected at 

 this volcano. Dr. Jaggar had great difficulty in finding a suitable source 

 for collecting, and greater difficulty in approaching it. The analysis of the 

 gases accounts for part of the difficulty, since they show 2 and 8 per cent of 

 vSOs respectively. The combustible gases had practically all disappeared 

 and the samples may be regarded as completely burned. It wi.l be noted, 

 however, that the amount of nitrogen present is not high and could not possi- 

 bly account for the amounts of water present, namely, 67 and 75 per cent 

 respectively. The argon group is present in rather larger amounts than at 

 Kilauea, but amounts to a maximum of only 0.6 per cent. Free sulfur 

 and chlorine were absent. Compared with similarly oxidized gases from 



