576 PETROLOGICAL ABSTRACTS AND REVIEWS 



"The Montezuma Mining District." The schistose rocks are described 

 as the Idaho Springs Formation and the Hornblende Gneiss Series. In 

 the former, quartz, biotite, and sillimanite are the most abundant minerals, 

 the most characteristic rock being called a mica- sillimanite schist. The 

 igneous rocks include three types of granite, porphyries of various sorts, 

 aplites, pegmatites, and a diabase. The ore deposits occur in several of 

 these rocks but their genetic relationships are not determined. 



"The Hahns Peak Region. " The igneous rocks include effusive rocks 

 and dikes ranging from rhyohte to olivine basalt, with plutonic diorite and 

 gabbro. Quartz basalt is found in several dikes in the western part of the 

 district. Extreme contact metamorphism is developed at the contact of 

 the porphyries with the sedimentary rocks. E. R. Lloyd 



Halle, G. "Neuer Hand-Demonstrationsapparat fiir alle Erschei- 



nungen der Doppelbrechung im Kalkspat," Zeit. Kryst., XL VII 



(1910), 376-77. 



Describes an apparatus for the demonstration of double refraction; 



the calcite prisms are smaller than those generally used, the desired effect 



being obtained by the use of a magnifying glass. For class work, the 



instrument is provided with a dicroscope and an aperture for mica wedge. 



W. T. SCHALLER 



Leiss, C. "Mikroskop mit gemeinsamer Nicoldrehung in verein- 

 fachter Form," Zeit. Kryst., XL VII (1910), 377-78. Fig. i. 

 A simple arrangement, suggested by Dr. F. E. Wright, by which both 

 nicols can be simultaneously rotated by means of a rigid vertical bar. 



W. T. SCHALLER 



Mackie, William. "The Distribution and Signification of 

 Deviations from the Normal Order of Crystallization, also the 

 Distribution and Significance of Micropegmatite in Granites, as 

 Illustrated by the Granites of the North of Scotland." Trans. 

 Edinburgh Geol. Soc, IX (1909), 247-317. Diagrams 6, photo- 

 micrographs 8. 

 The author found in previous microscopic investigations of granites 

 from the north of Scotland, that deviations from the normal order of crystal- 

 lization existed in almost every rock-slide examined, and the occurrence of 

 patches of micropegmatite was far more frequent than indicated in pre- 

 vious descriptions of such rocks. The present research was undertaken 



