Fairbanks.] 



Geology of Point Sal. 



43 



across the shore line diagonally. Following these dark rocks the 

 gabbro begins again, but is here very fine grained and almost porce- 

 lain like on the edges. As it is traced along the foot of the cliffs, it 

 is found to grow coarser again very rapidly, and in a few hundred 

 feet contains crystals of hornblende a half inch in diameter. Farther 

 along there is a small area in which it is regularly and beautifully 

 banded, a condition due to the arrangement of the light and dark 

 constituents in alternate layers a half inch in thickness. As we fol- 

 low the shore toward the east, the gabbro is again crowded down to 

 the shore, and for nearly 1,500 feet it appears as a narrow rim near the 

 edge of the water at low tide. The mountain above is occupied by 

 what appears to be the neck of a volcano. Immense masses of lava 

 in various conditions have fallen to the beach. In its essential 

 aspect this rock is a cemented basaltic breccia cut through and 

 through with gnarled and ropy lava injections. Scoriaceous and 

 amygdaloidal boulders appear inclosed in a slag-like matrix. 

 Aphanitic flows of different colors are mixed in confusion with 

 those of a spheroidal character. The twisted and curved rolls are 

 only a few inches in diameter, but not often scoriaceous. Epidote 

 as well as quartz is abundant in cavities and seams. Gnarled, pasty 

 and frothy masses of lava of all colors, yellow, red, green and black, 

 are mixed in the utmost confusion. The whole mass has been 

 seamed with calcite and weathers in the most rugged cavernous 

 fashion. The breaking up of a partially or wholly consolidated 

 magma and its repeated injection by streams of lava has probably 

 taken place in a manner similar to that observed in modern 

 volcanoes. 



Owing to the great mass of breccia which has fallen at the base 

 of the cliffs, it is rather difficult to say certainly whether the gabbro 

 has been forced up into the volcanic material or whether the latter 

 is the younger. It seems probable that the supposed volcanic neck 

 is the younger. The massive lava replaces the gabbro wholly in 

 places at the base of the cliffs, as shown by the exposures at low 

 tide. A little farther along and a body of gabbro appears inclosed 

 in the dark aphanitic rocks. It shows the effects of extreme 

 dynamical action in having been reduced almost to a powder, with 

 here and there small nodular masses of hard rock. East of the 



