1 82 PETROGRAPHICAL ABSTRACTS AND REVIEWS 



1838. It is an intermediate chondrite, with olivine and pyroxene as the 

 most important constituents. Metallic iron and nickel form nearly 6 

 per cent, and combined iron and nickel, 5 per cent. 



W. T, Schaller 



Dale, T. Nelson. ''The Cambrian Conglomerate of Ripton in 



Vermont," Am. Jour. Sci., XXX (1910), 267-70. Figs. 3. 



A conglomerate formed of pre-Cambrian pebbles generally held 



together in a highly metamorphosed " muscovite-quartz schist with 



more or less magnetite." The pebbles are a beach formation and are of 



local origin as is shown by their large size and by their similarity to 



adjacent rocks. 



Albert Johannsen 



Duparc, Wunder, and Sabot. "Les mineraux des pegmatites 



des environs d'Antsirabe a. Madagascar," Mem. Soc. Phys. 



et cTHist. Nat. Geneve, XXXVI (1910), fasc. 3, 283-410. 



The geology of Madagascar is briefly described and then, in detail, 



are described the rocks around Antsirabe. These include basalts, 



granites, quartz diorites, pegmatites, cipolines, quartzites, and mica 



schists. The localities of the pegmatites are then given in detail. The 



pegmatites occur chiefly in the cipoline and are formed principally of 



microcline and quartz, or plagioclase (near albite) and quartz. Mica, 



tourmaline, beryl, garnet, and pyroxene are also present. 



In the second part of the paper are mineralogical descriptions of 

 microcline, amazonite, lepidolite, lithionite (zinnwaldite), beryl (rose- 

 pink and aquamarine), tourmaline, spodumene, spessartite, garnet, and 

 cordierite from the mica schist of Mount Ibity. 



W. T. Schaller 



Grabham, G. W. "An Improved Form of Petrological Micro- 

 scope; with Some General Notes on the Illumination of Micro- 

 scopic Objects," Min. Mag., XV (1910), 335-49. Figs. 5; 

 pi. 1. 

 Suggests several improvements on a Dick microscope, namely, a 

 better adjustment for the condenser system, a triple nose-piece, iris 

 diaphragm, and a slot for introducing screens below the stage. The 

 graduated circle is placed below the ocular. Several other suggested 

 improvements have already been used on other microscopes. Several 



