GEOL. VOL. I.] SMITH SANTA CATALINA ISLAND. 63 



quite fresh and free from products of decomposition. The 

 mineral has a pronounced prismatic cleavage. _It is quite 

 strongly pleochroic, c being dark, greenish brown, 6 deep, 

 yellowish brown, and a very pale, brownish green. The 

 absorption scheme is c^l6>a. Inclusions are common, and 

 in many of the sections abundant. They are largely minute 

 flakes of a mineral with low polarization colors, and a 

 refractive index somewhat higher than that of the horn- 

 blende. The same mineral occurs in scattered flakes in the 

 garnets also, and they are there seen to be colorless or 

 nearly so. In the hornblende these flakes are in small, 

 open areas, usually collected near the center of the includ- 

 ing crystal. Besides these inclusions, occasional small 

 grains of rutile are found. 



The rutile, in general, through the slide, occurs as rounded 

 and usually oblong grains, in color deep yellowish to red- 

 dish brown, varying with the tints of amber. These grains 

 are usually found along the lines which mark the bounda- 

 ries between the hornblendes, and generally several together 

 occur along the same line. They have an extremely high 

 index of refraction, and on account of the consequent dif- 

 fusion of light the extinctions are not sharp and clear. The 

 direction of extinction in the grains which are distinctly 

 elongated is parallel and at right angles to the axis of elon- 

 gation. The mineral shows a pronounced though not 

 strong pleochroism, and has a strong absorption. As the 

 grains could not be distinguished from the dark hornblende 

 in the crushed rock, the hornblende was dissolved out by 

 means of hydrofluoric acid, when the minute, dark grains 

 of the rutile could be readily distinguished from the pale 

 red fragments of garnet, neither of these being attacked by 

 the acid. Some of these grains were then separated and 

 tested for titanium, with favorable results. 



The garnets have quite irregular boundaries, and along 

 the margin are frequently intergrown with the hornblendes 

 which surround them. In a number of cases minute frag- 

 ments of the garnets are completely enclosed by the border- 

 ing hornblendes, while occasionally a fragment of horn- 



