498 PETROLOGICAL ABSTRACTS AND REVIEWS 



Laitakari, Aarne. "Einige Albitepidotgesteine von Siidfinn- 

 land," Bull. Comm. Geol. Finlande, No. 51, 1918. Pp. 13, figs. 5. 

 The term helsinkite is proposed for a haphazard-textured dike-rock, consist- 

 ing of albite and epidote, and in some cases quartz (quartz-helsinkite). There 

 is, in some cases, a Uttle microcline, biotite, apatite, and iron ore. The amount 

 of epidote varies from 15 to 35 per cent. In the specimen analyzed there is 

 about 31 per cent epidote and 67 per cent feldspar, of which microcline forms 

 less than 5 per cent (see review of Makinen), consequently it belongs, in the 

 reviewer's system, to 21 12 (new form). Both albite and epidote are thought to 

 be primary magmatic minerals, the CaO having formed epidote rather than 

 anorthite in plagioclase on account of greater water content and lower temper- 

 ature of crystallization than the surrounding granite. 



Laitakari, Aarne. " tjber die Petrographie und Mineralogie der 

 Kalksteinlagerstatten von Parainen (Pargas)," Bull. Comm. 

 Geol. Finlande, No. 54, 192 1. Pp. 113, figs. 40, pis. 3. 

 The island of Alo, in South Finland, consists principally of migmatite, a 

 mixture of granite and gneiss. Within this rock are long, narrow lenses of 

 limestone, calcareous gneiss, and amphibolite, which represent remnants of 

 strata which were infolded in the igneous rock. Cutting all these rocks there 

 are granitic and basic dikes. A short introduction of 5 pages, descriptions 

 of rocks 28 pages, descriptions of minerals 57 pages, contact action 7 pages, 

 mineral paragenesis and metamorphism of the limestone 5 pages, and a bibliog- 

 raphy of 7 pages comprise the report. 



Larsen, Esper S. "The Microscopic Determination of the Non- 

 opaque Minerals, Bull. 6yg, U.S. Geol. Survey, Washington, 

 1921. Pp. 294. 

 In this very valuable bulletin, Mr. Larsen gives data for determining by 

 their refractive indices all of the transparent minerals recognized by Dana in 

 his System of Mineralogy as well as a considerable number not given by him. 

 Thus, if the optical properties are known, there is afforded a rapid means for 

 determining the minerals by immersion in liquid media of known indices. 

 Furthermore, about 125 pages give the results of new measurements of optical 

 constants of about 500 species for which data was not previously available. 

 The bulletin is invaluable and should be in the hands of every petrographer. 



Larsen, Esper S., and Hunter, J. F. "Mehlite and Other 

 Minerals from Gunnison County, Colorado," Jour. Washington 

 Acad. Sci., IV (1914), 473-79. 



While this paper is principally mineralogic, here is first proposed the new 

 name uncompahgrite, from the Uncompahgre quadrangle, Colorado, where the 



