CLASSIFICATION OF IGNEOUS ROCKS 221 



basalt or mela-melilitite of farrisite. There are also analcite- 

 basalts, most of which belong in this family, though some fall in 

 Class 2. 



CLASS 3, ORDER 2 



(327) Melagranite. See note under (127). 



(328) Mela-adamellite. See notes under (127) and (228). 



(329) Melagranodiorite. See notes under (127) and (229). 

 (3210) Melatonalite. See notes under (127) and (2210). 



(3212) Melasyenite. See notes under (127). Some years ago 

 Weed and Pirsson^ described a rock from the Highwood Mountains 

 as containing about equal amounts of light and dark constituents, 

 and gave to it the name yogoite. Their series of rocks as given was : 



All orthoclase, no augite = sanidinite. 



Orthoclase exceeds augite = augite-syenite. 



Orthoclase equals augite = yogoite. 



Augite exceeds orthoclase = shonkinite. 



All augite, no orthoclase = pyroxene and peridotite rocks of various types. 



Later^ they withdrew the name yogoite since they found that it 

 fell into Brogger's monzonite group on account of the proportions 

 of orthoclase and plagioclase. The original yogoite, computed 

 in the present system, falls in (2212) and is a normal monzonite, 

 but associated with it, on Yogo Peak, and called shonkinite^ by 

 Weed and Pirsson, are two other rocks which differ from normal 

 shonkinites in being associated with quartz-bearing instead of with 

 feldspathoid-bearing rocks and in containing andesine instead of 

 albite. They also contain more soda-orthoclase than andesine. 

 These "shonkinites," therefore, may well take upon themselves 

 the discarded name yogoite, since they also occur on Yogo 

 Peak, and fit into the foregoing scheme even better than the 

 original yogoite. 



(3213) Melamonzonite. See note under (127) and (2213). 

 Here belongs a basic contact monzonite of the Coryell bathohth, 



'W. H. Weed and L. V. Pirsson, "Igneous Rocks of Yogo Peak, Montana," 

 Amer. Jour. Sci., L (1895), 479. 



^ W. H. Weed and L. V. Pirsson, "The Bearpaw Mountains of Montana," Amcr. 

 Jour. Set., I (1896) 357-58. 



3 L. V. Pirsson, "Petrography of the Igneous Rocks of the Little Belt Mountains, 

 Montana," U.S. Geol. Stirv., Ann. Rept., XX, Part III (1900), p. 487. 



