364 HENRY S. WASHINGTON 



orthoclase around labradorite cores is also noteworthy; a feature 

 which we have met with so often in the Italian rocks. The 

 most basic of them — the absarokites with silica from 47 to 52 

 and very high magnesia and lime — carry olivine, as do the 

 more acid shoshonites with silica from 50 to 56; these latter 

 correspond to the Italian ciminites. The last of the series — the 

 banakites with silica from 51.5 to 61 — carry no olivine, and 

 more biotite than augite, and are rather poor in ferromagnesian 

 minerals ; these would correspond to some of the vulsinites. It 

 is especially worthy of note that in these last rocks "augite and 

 olivine are more or less completely replaced by biotite" — the 

 same mutual exclusion being observed here that we find in 

 Italy. Chemically the absarokites are much more basic, while 

 the analyses of the shoshonites and banakites closely approxi- 

 mate to those of the ciminites and vulsinites, except in the 

 alkalies. 



The similarity is indeed so great that the ciminites might 

 with propriety be called shoshonites, and the vulsinites banakites. 

 But there are certain considerations which seem to render such 

 a course inadvisable. The difference in the alkalies has been 

 already mentioned. While in the Italian rocks they are high 

 and with potash very largely preponderating over soda, in the 

 American rocks they are rather lower, and soda, while always 

 lower in percentage, is much closer to the potash and molecu- 

 larly often surpasses it. In Italy again we find the acid tos- 

 canites which are not represented at the Yellowstone Park, 

 while at the latter we have the absarokites and nothing corre- 

 sponding to them in acidity among the trachydolerites of 

 Italy. The center of acidity, so to speak, at the Yellowstone 

 Park seems to lie quite low, while in Italy it is much higher. 

 Furthermore the great abundance of leucite at the Italian vol- 

 canoes is unparalleled in the American district, where the absaro- 

 kite-banakites are genetically related to normal andesites and 

 basalts, though leucite occurs to a small extent.^ From these 



'RosENBUSCH, in the last edition of his Mikroscopische Physiographic (II, 1216, 

 1896), describes these rocks in connection with the leucite-tephrites. 



