GEOL.-VOL. I.] SMITH SANTA CATALINA ISLAND. 25 



obliterated by decomposition products. Hornblende is 

 wholly replaced by chloritic material. 



Analysis. The porphyrite was nowhere found in an en- 

 tirely fresh condition. The following analysis was made 

 from the freshest specimen obtained, as shown by its thin 



section: 



I. II. 



SiO 2 ............................ 63.82 65.71 



Ti O 2 . . . . ....................... trace 



A1 2 O 3 ........................... 16.53 i7- 8 



Fe 2 O 3 ........................... 1.28 2.84 



Fe O ............................ 2.93 1.79 



MnO ........................... trace 



Ca ............................ 5-57 5-24 



Mg O ............................ 1.99 2 -57 



Na 2 O ........................... 4.12 3.87 



K 2 O ............................. 77 1-02 



H 2 ............................ 1.82 



C O ............................ 1. 10 



99.93 100.12 



Sp. gr ............ .............. 2.689 



I. Porphyrite from Pebbly Beach, Santa Catalina. 

 II. Quartz-diorite, Dognaska. (Banatite.) 



The analysis of the porphyrite differs but little from that 

 of the banatite given above. In some of its aspects the 

 diorite is not much unlike the microscopic character of 

 some of the banatites. 



Inliers of Basement Rocks. At a number of points in the 

 porphyrite area, following the general direction of the main 

 ridge to the west of Avalon, and along a line extending 

 from the coast northwest of Avalon to near the coast east of 

 Silver Canon, there occur at intervals patches of the base- 

 ment rocks. These are found not only along the main crest, 

 but on several of the branch ridges to the west and north- 

 west of Avalon, and on one of the branches running into 

 Silver Canon. They also occur at irregular intervals at the 

 base of the cliffs, from Avalon Harbor for a distance of 

 about a mile to the northwest. The outcrops along the 

 ridges vary from a few yards to nearly 200 feet in length. 



