DALY. — COMPOSITIONS OF IGNEOUS-ROCK TYPES. 215 



9- Analyses of Rocks from the Laboratory of the United States Geo- 

 logical Survey, 1880 to 1903, by F. W. Clarke. Bulletin 228 

 of the Survey, 1904. 



10. Geological and Petrographical Studies of the Sudbury Nickel Dis- 



trict, by T. L. Walker, Quart. Jour. Geol. Soc, Vol. 53, 1897, 

 p. 40. 



11. Petrography and Geology of the Igneous Rocks of the Highwood 



Mountains, Montana, by L. V. Pirsson. Bull. 237, U. S. Geo- 

 logical Survey, 1905. 



12. Geology of the North American Cordillera at the Forty-ninth 



Parallel, by R. A. Daly (forthcoming ; analyses by M. F. Con- 

 nor and M. Dittrich used in calculating some averages). 

 The sources of the analyses used in each average are indicated by the 

 authors' names at the head of the corresponding columns in Table II. 



