Fairbanks.] 



Geology of Point Sal. 



61 



Figure 7. — In the center are shown angular fragments of serpentine inclosed 

 in a gabbro dike. 



vicinity of the greatest development of the diabase dikes considera- 

 ble movement has taken place, and veins of pectolite fill the seams. 

 They are most abundant in the diabase and along the contact. 

 South of the Head a dike of olivine-rich gabbro occurs in the ser- 

 pentine. Near the southern end of the cliffs there is an interesting 

 series of gabbroitic dikes. The following section is shown : First 

 a gabbro dike 200 to 300 feet wide, then a few feet of dark, sheared 

 serpentine containing nodular masses of a hypersthene gabbro, 

 probably a dike broken up by movement; after this an irregular 

 dike of gabbro two to five feet wide, followed by another of picrite, 

 and that by a dike of troctolite; serpentine at last terminates the 

 series, disappearing beneath the debris. At several spots there 

 were noted dikes intermediate in character between the gabbros and 

 peridotites, which were later than the peridotite, but there are good 

 examples of distinctly gabbroitic dikes intrusive in the dunite. 



The last and deepest of the canons which have been eroded 

 across this eruptive complex is that leading up to the dairy and the 

 old gypsum mines. A section is shown here quite similar to that 

 farther west. At the northern side there are diabasic dikes of dif- 



