Fairbanks.] 



Geology of Point Sal. 



91 



EXPLANATION OF PLATE 2|. 



The letters in the illustration refer to the following minerals: F, feldspar; 

 P, pyroxene; A, analcite and its alteration products; M, magnetite; G, glass. 



Figure i. — Volcanic ash in the lower Miocene, showing the pumiceous glass 

 occasionally inclosing feldspars, x 20. 



Figure 2. — Augite-teschenite in which the feldspars are partially replaced by 

 a pegmatitic intergrowth with secondary feldspar. > 20. 



Figure 3. — Panidiomorphic facies of the augite-teschenite. The analcite 

 occurs in large areas bounded by the idiomorphic faces of the 

 other components. The magnetite is later than both augite 

 and feldspar, x 20. 



Figure 4. — Large augite plate with poikilitic structure. There are shown 

 seven small polyhedral areas of altered analcite, partly in con- 

 tact with the augite and partly inclosed in the feldspars, x 21. 



Figure 5. — A large plate of augite containing feldspar crystals of various 

 sizes and often showing jagged terminations. Disconnected 

 areas of altered analcite appear in the center of the augite crystal 

 and are bounded in part by crystallographic planes of the latter. 



x 20. 



Figure 6. — Another of the poikilitic augite crystals from the teschenite. Is 

 contains small lath-shaped feldspars, while on one edge there is 

 a large area of analcite which penetrates the augite and it 

 bounded by crystal planes of the latter, x 20. 



