PETROLOGICAL ABSTRACTS AND REVIEWS 575 



Daly, Reginald A. "Origin of the Alkaline Rocks," Bull. Geol. 

 Soc. America, XXI (1910), 87-118. 



No alkaline province can be described as free from subalkaline erup- 

 tives, especially those of basaltic or granitic types. Emphasis is laid on 

 the indisputable fact that the visible volume of all alkaline rock bodies is a 

 very minute quantity as compared with the visible volume of subalkaline 

 eruptive bodies. An inductive study shows that most alkaline rocks cut 

 thick masses of limestones, dolomites, or other calcareous sediments. A 

 long table illustrates the association. This fact suggests the hypothesis 

 that the absorption of carbonate disturbs the chemical equilibrium of sub- 

 alkaline magma in such manner that alkaline fractions are produced by 

 differentiation. Most of the alkaline species are ascribed to the interaction 

 of basaltic magma and limestone (or dolomite), but more acid magma is 

 also sensitive to the solution of carbonate. The hypothesis explains the 

 concentration of alkalies; the desilication shown by the crystallization of 

 nephelite, leucite, corundum, etc. ; the extreme variabihty of alkaline bodies 

 in mineralogical and chemical composition; the occurrence of such lime- 

 bearing minerals as melilite, scapolite, woUastonite, melanite, etc., and 

 COz-bearing minerals as cancrinite and primary calcite. Suggestions are 

 offered as to some of the chief physico-chemical reactions involved. — 

 (Author's Abstract.) 



George, R. D., State Geologist, and Others. Colorado Geological 

 Survey, First Report, 1908. 



The report contains the following papers: "The Main Tungsten Area 

 of Boulder County," by R. D. George, with notes on the intrusive rocks 

 by R. D. Crawford, pp. 7-104; "The Montezuma Mining District of 

 Summit County," by H. B. Patton, pp. 105-44; "The Foothills Forma- 

 tions of Northern Colorado," by Junius Henderson, pp. 145-88; "The 

 Hahns Peak Region, Routt County" (an outline survey), byR. D. George 

 and R. D. Crawford, pp. 188-229. 



"The Tungsten Area of Boulder County." The ores are found in 

 veins in a region of biotite granite and granitic gneiss, the latter grading 

 into quartz-mica schist and mica schist. These older rocks are cut by 

 dikes and irregular bodies of granite and both coarse and fine pegmatite. 

 In the northern and western parts of the district are many dikes which are 

 described by R. D. Crawford as dacite, latite, latite porphyry, andesites of 

 various sorts, diabase, basalt, basalt porphyry, lamprophyre, pyroxenite, 

 and limburgite. 



