522 WHITMAN CROSS 



NORMS OF ROCKS COMPARED WITH THE HAWAIIAN TRACHYTE— (Co»r 



Essex county, Mass., where there is a great variety of rocks, dis- 

 cussed in their genetic relations by Washington. ' No one of the rocks 

 of the table occurs in an association comparable with that of the 

 Hawaiian trachyte. The occurrence here described seems to be a 

 notable one, requiring consideration from the advocates of the view 

 that a natural or genetic classification of igneous rocks may be worked 

 out from the study of their associations. The recent tabulations o'f 

 chemical analyses of igneous rocks by Washington^ and Iddings,^ 



1 "The Petrographic Province of Essex County, Mass.," Journal of Geology, Vols. 

 VI and VII (1898, 1899). 



2 "Chemical Analyses of Igneous Rocks, 1884-1900," Professional Paper No. 14 

 (1903), U. S. Geological Survey; "The Superior Anlayses of Igneous Rocks from 

 Roth's Tabellen, 1869-1884," Professional Paper No. 28 (1904), U. S. Geological 

 Survey. 



3 "The Chemical Composition of Igneous Rocks, Expressed by Means of Dia- 

 grams, etc.," Professional Paper No. 18 (1903), U. S. Geological Survey. 



