PETROLOGICAL ABSTRACTS AND REVIEWS 463 



and in particular those of Maine, local descriptions by counties, and 

 descriptions of the economically important minerals. 



Granite-pegmatites are defined here as differing but little from the 

 granites of the state in mineral composition, but are characterized, not 

 necessarily by coarse, but by extreme irregularity of grain. They 

 occur in dikes or sill-like masses, generally of sheet-like form and some- 

 times of considerable size. The contact with the country rock is gen- 

 erally sharp, indicating very little assimilation by the pegmatite even 

 where it is of batholithic dimensions. Contact metamorphism around 

 the pegmatites is no greater than that near granite contacts, and indi- 

 cates, according to the writer, that the amount of mineralizers present 

 was but little greater than in the latter rocks; less than ten times as 

 great, probably. Genetically the pegmatites are related to the asso- 

 ciated granites and are probably contemporaneous with them. Where 

 particularly abundant, they form, apparently, the roofs above granite 

 batholiths. An examination of the quartz grains indicates, in the 

 coarser varieties, that the crystallization began slightly above 575 C. 

 and ended at a lower temperature. The finer-grained varieties may 

 have crystallized entirely above 575°. 



Among the minerals of economic importance found in the Maine 

 pegmatites are the feldspars, orthoclase and microcline rose and smoky 

 quartz, amethyst, muscovite, tourmaline, beryl of various colors, and 

 topaz. The occurrences, compositions, properties, and uses of these 

 minerals are discussed. 



Albert Johannsen 



Cotjyat, J. "Les roches sodiques du desert arabique," Comptes 

 Rendus de VAcademie des Sciences, CLI (1910), 1 138-41. 



In a region east of the Nile, near longitude 34 18' E., latitude 24 

 40' N., there are dikes and stocks of nepheline syenite with much varia- 

 tion in texture, also tinguaite and solvsbergite. Four analyses of the 

 syenite show Si0 2 60.1 to 56.5 per cent; Na 2 9.0 to 10.6 per cent; 

 K 2 4.5 to 5.2 per cent; Fe 2 3 , FeO 3.2 to 6.1 per cent; very low 

 MgO and CaO. In the quantitative classification the rocks are mias- 

 koses and laurdaloses. 



The syenites are related to volcanic eruptives of Cretaceous age 

 and posterior to a series of trachytes, andesites, and basalts. 



F. C. Calkins 



