770 ALEXANDER N. WINCHELL 



name zirkelite for a devitrified basalt, basaltic tuff, or tachylyte; 

 devitrified obsidian they called an apobsidian, and a devitrified 

 rhyolite an aporhyolite, as suggested by Bascom. Wadsworth's 

 quartz biotite diorite is called syenite by Grant. It is an intermediate 

 type corresponding to a monzonite. 



The quantitative classification of igneous rocks as proposed by 

 Cross, Iddings, Pirsson, and Washington may be used as the basis 

 of a correlation of the Keweenawan igneous rocks. From a chemical 

 point of view such a correlation (see Table III) is more exact than 

 one based upon the mineral composition and texture, but it can 

 include only those rock types of which satisfactory quantitative ana- 

 lyses are available. 



An examination of the table of correlation on this basis will 

 reveal the fact that the number of satisfactory analyses available is 

 not great, especially when compared with the descriptions previously 

 mentioned. Several of the early analyses are not included in the 

 tabulation because of manifest inaccuracy or incompleteness. 



The analyses of Streng and Pumpelly are good for the time at 

 which they were made. The norm of Pumpelly's andose is: or 7 . 78, 

 ab 42.44, an 17.24, hy 1.30, ol 17.97, mt 4.41, il 4.41. The norm 

 of his camptonose is: or 7. 23, ab 22.01, an 23.91, ne 4.26, di 22.55, 

 ol 7.47, mt 4.18, il 5.32. The norm of his auvergnose is: or 0.56, 

 ab 16.24, an 36.97, di 15.88, hy 20.34, ol i.ii, mt 3.71, il 1.98. 

 Sweet published two analyses of Keweenawan rocks; the one of 

 diabase from the Ashland mine, Ashland Co., Wis., is wholly unsatis- 

 factory; the other is approximately correct, and classifies as hessose. 

 The analyses of gabbros published by Wadsworth are recalculated 

 in Washington's tables' of chemical analyses of igneous rocks; the 

 norm of his diabase granophyrite from the Cleveland mine is : Q 5 . 10, 

 or 8.34, ab 16.77, an 32.25, di 11.02, hy 9.90, mt 8.45, il 5.17; 

 the norm of his sample from Houghton Co. is: Q 8.46, or 8.90, 

 ab 23.06, an 16.40, di 13.75, ^Y 20.82, mt 5.80, apo.34. Washing- 

 ton's tables give full details regarding the recalculation of the analyses 

 of Keweenawan rocks pubhshed by Van Hise, N. H. Winchell, and 

 Bayley. The norms of the analyses reported by Hubbard may be 

 summarized as follows: 



I H. S. Washington, U. S. G. S., P. P. 14, 1903- 



