PETROLOGICAL ABSTRACTS AND REVIEWS 499 



rock was found. It is a coarse-grained rock made up of about two-thirds 

 or more melilite, with considerable pyroxene, magnetite, perofskite, and apa- 

 tite, while in places biotite, calcite, and other minerals occur. In texture it 

 is commonly coarse, but varies. Cleavage pieces of melilite a foot across and 

 mottled by inclusions of other cpnstituents are not uncommon. The finest 

 grained rock is hypautomorphic-granular with crystals averaging i mm. 

 across. In the new system of the reviewer, the rock belongs to 2125. 



Larsen, Esper S., and Mansfield, George R. "Nepheline 

 Basalt in the Fort Hall Indian Reservation, Idaho," Jour. 

 Washington Acad. Sci., V (191 5), 463-68. 



The mode of this nephelite-basalt, as given by Mr. Larsen, is nephelite 20, 

 diopside 39, forsterite 26, biotite 8, magnetite 3, ilmenite i, and apatite i per 

 cent. In the reviewer's system it belongs in 3125 (new form). 



Lehmann, E. "Die Ermittlung der Brechungsexponenten der 

 Mineralien im Diinnschliff durch Vergleich mit Canadabalsam 

 und KoUolith," Centralbl. f. Min., etc., (1921), 102-12. 



The refractive index of Canada balsam in certain slides was foxmd to be 

 lower than the recently accepted values, being less than 1.5243. A series of 

 experiments with KoUolith showed that the refractive index depended upon the 

 original solvent and upon the temperature of heating. With hard koUolith 

 and a temperature of 150° to 156°, the resulting moimt was found to have prac- 

 tically a constant value of 1.533S, but with koUolith dissolved in xylol exposed 

 to air, or under cover-glasses, the values varied from 1.5 19 to 1.5343, though 

 the first averaged values between 1.5 231 to 1.5343 and the latter 1.5257 to 

 1.5298, depending upon the time of exposure to the air, the higher values being 

 obtained after about six weeks. 



Lynes, Hubert, and Smith, W. Campbell. "Preliminary Note 

 on the Rocks of Darfur." Geol. Mag., LVIII (192 1), 206-15. 

 The author describes rocks from the volcano of Dereiba and from various 

 other points between there and El Obeid, Africa. None from this area has 

 previously been described. Troctolite, granite, graphic granite, sandstones, 

 gneisses, and quartz-monzonite occur on the road. The rocks of the volcano 

 are quartz-bearing soda-trachyte, soda-trachyte, quartz-bearing riebeckite- 

 trachyte, andesine-bearing kenyte, and mugearite. 



Makinen, Eero. "Oversikt av de Prekambriska Bildningarna i 

 Mellersta Osterbotten i Finland," Bull. Comm. Geol. Finlande, 

 No. 47, 1916. Pp. 152, map I, figs. 25. 

 The pre-Bothnian rocks of the district described are represented by two 



small areas of ortho-gneisses. The Bothnian complex consists of plagioclase- 



