ELKHEAD MOUNTAINS. 179 



Magnesia 10.13 9.89 



Lithia trace trace 



Soda , 3.77 3.84 



Potassa 1.65 1.68 



Phosphoric acid 0.11 0.11 



Ignition 1.30 1.30 



99.79 99.53 



Anita Peak has at its summit a curiously-castellated knob, rising sev- 

 eral hundred feet above the level of the main ridge, made up of very dis- 

 tinctly columnar basalt. The columns are very irregularly arranged, being 

 sometimes horizontal, sometimes perpendicular, but in general having a 

 somewhat radial arrangement. The rock of the peak has a strong influence 

 upon the magnetic needle, which, at the summit, points east instead of north. 

 The basalt, of which the peak is composed, is an almost black, rather com- 

 pact rock, very rich in olivine, which occurs in very large, well-defined crys- 

 tals, and, where decomposed near the surface, imparts a rusty color to the 

 mass. Under the microscope, it is seen to have an amorphous glassy base, 

 and to belong to the feldspar-basalts. It contains well-striated plagioclases, 

 dark-brown augites, and magnetite grains. 



The broad, flat-topped mass of Mount Weltha, though higher than any 

 of these volcanic peaks, does not give the impression of so great altitude to 

 the observer on account of its long, gentle slopes, and the absence of a 

 sharp summit-peak. The basalt presents much the same general character, 

 but on its western foot-hills is more porous, of a somewhat lighter color, and 

 has the texture of a dolerite. This rock is remarkably rich in olivine, and, 

 under the microscope, is seen to contain magnetite, augite, and nepheline, 

 with well-defined crystals of sanidin, sometimes in Carlsbad twins The 

 nepheline is not crystallized, but forms a sort of base, as is generally the 

 case with these nepheline-basalts. The presence of sanidin in this connection 

 is very remarkable, especially as the rock contains no plagioclase at all. 



From the extreme western foot-hills of Mount Weltha, there extends out 

 into the red Tertiary plains, in a direction a little north of west, a curious 

 wall, so straight and regular that it would seem to be built of masonry. It is 



