112 GE0L0G1 OF THE HIGH PLATEAUS. 



The foregoing scheme of classification is in the following conspectus 

 given as a whole. Of the various sub-groups the following have not yet 

 been detected among the eruptives of the High Plateaus : nevadite, por- 

 phyritic trachyte, augitic propylite, dacite, nephelin-dolerite, leucite-basalt, 

 nephelin-basalt. All of the others are well represented. The trachytic 

 group, however, very far overshadows all the others in volume and variety. 



Group I. — Acid rocks. Ehyolites. 



Sub-groups. 



1. Nevadite. 2. Liparite. 3. Rhyolite (proper). 



Gkoup II. — Sub-acid kocks. Trachytes. 



Sub-group A. — Sanidin trachytes. Sub-group B. — Hornblendic trachytes. 



1. Granitoid trachyte. 5. Hornblendic trachyte. 



2. Porphyritic trachyte. C. Augitic trachyte. 



3. Argilloid trachyte. 7. Phonolite. 



4. Hyaline trachyte. 8. Trachytic obsidian. 



Group HI. — Sub-basic rocks. Andesites. 

 Sub-groups. 



1. Hornblendic propylite. 4. Hornblendic andesite. 



2. Augitic propylite (!). 5. Augitic andesite. 



3. Quartz propylite. 6. Dacite. 



Group IV. — Basic rocks. Basalts. 

 Sub-grouj)s. 



1. Dolerite. 4. Leucite basalt. 



2. Nepheliu dolerite. 5. Nephelin basalt. 



3. Basalt (proper). 6. Tachylite. 



