ULTEA-BASIC INTRUSIVES. 215 



the light-yellow to greenish tones of actinolite, although its character is 

 more that of the compact hornblende. In one case its secondary nature 

 was shown by the presence of a small irregular area of brown hornblende 

 lying in a mass of the green. The two have the same orientation. In this 

 case the chlorite is apparently a tertiary product, the original mineral 

 being the brown hornblende, from which was formed the light-green variety, 

 which in its tui'n alters to the chlorite. 



Between the various pseudomorphs are irregular plates of compact, 

 dark-brown hornblende, plates of biotite, large crystals of magnetite, and 

 rough branching agg-regates of ilmenite. These, while molded on the 

 phenocrysts, themselves lie in the chloritic mass already mentioned, which 

 also often completely surrounds the phenocrysts, and which is probably an 

 altered vitreous base. 



The pieces of brown hornblende which remain unaltered show moder- 

 ately strong pleochroism, reddish brown for c and Ij and light brownish 

 yellow for a. C^ll>(l. This hornblende contains inclusions of iron oxide 

 and has all the appearance of an original mineral. By alteration it passes 

 through a compact greenish amphibole to a much lighter colored, reedy, 

 actinolitic variety of amphibole. In the secondary amphibole occur certain 

 golden-brown grains with high single and double refracti6n, which are 

 supposed to be rutile formed from the hornblende, and also some brown 

 transparent plates of ilmenite. The orientation of the secondary horn- 

 blende is the same as the original. No further alteration of this amphibole 

 was observed, but it is believed that the prismatic crystals altered to 

 chlorite, calcite, and magnetite, as described above, are the extreme cases 

 of alteration of an automorphic form of a brown hornblende very similar 

 to the part described. 



The biotite between the phenocrysts is in ragged areas either surround- 

 ing iron oxide or associated with it or with the hornblende. It is very 

 pleocln"oic, the absorption parallel to the basal cleavage being so strong as 

 to render the section opaque. Perpendicular thereto the color is a dark 

 chocolate brown. The mica does not show its usual bright polarization 

 colors in sections cut parallel to crystallographic c. This may be due in 

 some measure to the very strong absorption. In some cases the biotite is 

 seen to have a strong blue to violet metallic luster in incident light. The 

 biotite has partly altered to chlorite. The alteration proceeds along the basal 



