574 PETROLOGICAL ABSTRACTS AND REVIEWS 



tact metamorphism (at Bethel the magma under pressure sent out stringers 

 into the wall rock; at Barre, the constituent elements, quartz, feldspar, 

 biotite, pyrite, apatite, etc., were injected as heated vapors along the 

 cleavage foliation); orbicular texture in granite at Bethel — the nodules 

 occur in sheets parallel to the flow structure and the major axes of the 

 disks are parallel to the micaceous flowage bands; and delimonitization on 

 the under side of the sheets of granite. 



Part II, while chiefly economic, touches on the general geology of the 

 areas, gives petrographical descriptions of rocks, and economic details of 

 the quarries. The work concludes with a bibliography of the literature on 

 granites and a glossary of rock and quarry terms. 



Charles J. Hares 



Daly, Reginald A. "Average Chemical Compositions of Igneous- 

 Rock Types," Proc. Amer. Acad. Arts and Sci., XLV (1910), 

 211-40. 

 Using Osann's "Beitrage zur chemischen Petrographie " and a few 

 other sources, the average chemical composition of 98 principal igneous- 

 rock types (excluding ascitic dikes) has been calculated. The results are 

 shown in a table which also gives the averages for the same rocks regarded 

 as anhydrous. These averages are of use in showing the chemical "center- 

 points" in Rosenbusch's classification, the one in general use by the makers 

 of geological maps. The averages furnish one of the bases for finally 

 calculating the "average igneous rock." The relative uniformity in the 

 soda percentage of the more abundant types is specially noted in its bearing 

 on the origin of oceanic sodium and, therewith, on the problem of the age of 

 the earth. The striking similarity of the average granite analysis to the 

 average analysis of the base (ground-mass) in augite andesite, and the 

 equally close resemblance of the average diorite analysis to the arithmetical 

 mean of average basalt and granite are illustrated. The table of averages 

 shows that the effusive rocks are more salic than the corresponding plutonics, 

 helping to prove the justice of Rosenbusch's primary subdivision of igneous 

 rocks into deep-seated types and surface lavas. The difference is explained 

 genetically. Other special points in classification are noticed. The 

 essential identity of the averages for pre-Cambrian and post-Cambrian 

 granites is referred to the "anchi-eutectic" nature of the type. — (Author's 

 Abstract.) 



