Geol— Vol. I.] SMITH— SANTA CATALINA ISLAND. 1 7 



the quartz. The simultaneous development with the quartz 

 is evidenced by a frequent irregular intergrowth along the 

 boundary line of the two minerals, and further by the occa- 

 sional development of micropegmatitic structure. 



Quartz occurs in somewhat smaller individuals than do the 

 feldspars. It is most frequently found in aggregations or in 

 lines, as if, being the last mineral to form, it had filled the 

 spaces between those previously existing. It is present in 

 varying amount in all the slides, being fairly abundant in 

 some, amounting to perhaps one-fourth of the total minerals 

 of the slide. The sections vary in size from about .1 mm. 

 to about 1.2 mm. It occurs in allotriomorphic forms, usu- 

 ally with very irregular outlines, the sections being fre- 

 quently somewhat intergrown on the margins. The sections 

 are usually clear. Most of them contain liquid inclusions, 

 occurring usually without any definite arrangement, though 

 occasionally they are seen in lines extending through several 

 sections. Besides these there may be seen with the higher 

 powers occasional minute, greenish needles, and sections 

 having the form of cross-sections of hornblende. They 

 are without noticeable polarization. The quartz also con- 

 tains occasional magnetite. 



The hornblende occurs in sections with very irregular 

 boundaries, due to resorption. No approach to crystal 

 forms was seen. The feldspar is always moulded on the 

 hornblende, except in one case observed. In this section a 

 small crystal of feldspar was seen apparently projecting into 

 one side of the hornblende, the feldspar showing good 

 crystal boundaries where surrounded by the hornblende. 

 Aside from this instance the hornblendes contain no inclu- 

 sions of feldspar, while the feldspars contain occasional 

 inclusions of hornblendic material. The smaller feldspars 

 are doubtless, in part, at least, contemporaneous with the 

 hornblendes, though the feldspars in general are later. In 

 size the former compare favorably with the feldspars. 

 Twinning parallel to the orthopinacoid is common in the 

 larger and fresher sections. The pleochroism is pronounced, 



( 2 ) January 9, 1S97. 



