458 II. W. Turner — Lavas of Mt. I?igaUs, California. 



breccia. Wherever in the Sierra Nevada its relation to the 

 andesite is evident, it is the older rock. The relative age of 

 the rhyolite and the older basalt has not been made out. I 

 have nowhere seen them in juxtaposition. 



It is expected that the above rocks will be studied in more 

 detail later, with the aid of chemical analyses, so that their 

 exact position in the series of Tertiary lavas may be deter- 

 mined. The subject is of especial interest in relation to 

 Richthofen's law of succession of volcanic rocks, to which 

 this forms an apparent excej)tion. 



The subject of the succession of the igneous rocks of the 

 Great Basin has been considered in detail by Hague in the 

 forthcoming monograph of the IT. S. Geological Survey on 

 the Eureka District, Nevada, and by Iddings* who states that 

 igneous rocks of a mean composition are usually followed by 

 both highly basic and highly acid types. 



The Tertiary lavas of Mount Ingalls rest on a base of much 

 older rocks, schists, metamorphic tuffs and granite. The latter 

 rock is of igneous origin, as is shown by the inclusions in it of 

 the older clastic rocks which are here in part at least, of Car- 

 boniferous age. These inclusions are numerous at a point on 

 the southwest slope of the mountain, three miles from the 

 summit. 



Since writing the above, the following analyses have been 

 obtained : 



Older basalt Late basalt 

 (No. 276.) (No. 311.) 



Si0 2 50-56 53-91 



TiO; 1-71 -52 



A1„0 3 .- 14-71 17-95 



Fe"„0 3 3-54 2-21 



Feb 8-90 4-80 



MnO -13 -10 



CaO 7-58 10-40 



SrO trace ? trace. 



BaO .,_ -25 -05 



MgO... 4-07 5-52 



K 2 2-10 1-34 



N 2 2-94 2-90 



Li 2 trace ? trace. 



H 2 at 100° C 1-06 -20 



H 2 above 100 C 1-12 -20 



P.O. 1-14 -21 



99-81 100-31 



*"The Origin of Igneous Rocks," by J. P. Iddings, Bull. Phil. Soc. Wash- 

 ington, vol. xii, pp. 89-214. 



