22 



University of California. 



[Vol. 2- 



the structure is not noticed until shown by reflection from a cleav- 

 age plane. In this facies the feldspars are invariably very small,, 

 while the augites occasionally reach a size of 1.5x1 inch. The lines 

 of weakness in the rock, or those along which greater alteration 

 has taken place, seem to lie between the augites. The large boul- 

 ders strewn along the base of the cliffs almost always weather with 

 pitted surfaces due to the aggregation in bunches of some more 

 easily decomposed constituent. In some cases the softer spots 

 consist largely of greenish material, which, however, appears to be 

 distinct from the augite. In other rocks the lighter-colored por- 

 tion appearing in nodular forms several inches in diameter, weather 

 away more rapidly. 



The surface of the cliffs is far from having a uniform appear- 

 ance. In addition to the variation in color there appear large 

 irregular bunches or ramifying dike-like masses of rock which are 

 much more coarsely crystalline. In some cases these appear 

 sharply differentiated from the body of the rock; at others they 

 gradually blend into it. Scattered through portions of the coarser 

 rock, and in the centers of the ramifying dike-like masses, are cavi- 

 ties which are lined with finely crystallized analcite. The crystals 

 are clear and often perfectly formed, showing the common trap- 

 ezohedral shape. This type does not seem to have been subse- 

 quently intruded but to be a kind of segregation from the magma, 

 cooling more slowly, and probably formed after the consolidation or 

 partial consolidation of the main mass. It might be due to strain 

 set up in the partly consolidated magma resulting in a partial 

 refusion and followed by slow cooling. 



The dike-like masses of somewhat lighter color ramifying 

 through the dark rock at first sight appear like true dikes, but 

 upon close examination they present a different character. They 

 are generally very coarse, with large augite crystals standing on 

 their borders perpendicular to the walls and interlocking with the 

 constituents in the inclosing rock. There is no sharp line between 

 the two. Some of the augites reach a length of four inches and a 

 diameter of over a half inch, frequently showing idiomorphic boun- 

 daries, and inclosing a correspondingly coarse mass of feldspar. 

 The central portions of these areas of coarse crystallization, which it 



