64 CALIFORNIA ACADEMY OF SCIENCES. [PROC. 30 SER. 



blende is wholly surrounded by the garnet near its margin. 

 Frequent cracks, many of them iron -stained, intersect the 

 garnets, without definite direction. Macroscopically the 

 garnets appear to have a zonal structure, with a narrow and 

 somewhat clouded outer zone, a broad middle zone, seem- 

 ingly of the clear pink garnet, and a slightly darker inner 

 zone. Under the microscope this structure is seen to be 

 due to inclusions in the garnet. With crossed nicols the 

 sections are, as a whole, not perfectly isotropic, but trans- 

 mit a faint light in all positions. This is due to a multitude 

 of microscopic, dust-like inclusions, which fill the central 

 portions of the garnets. With higher powers these inclu- 

 sions cannot be resolved, but are seen to be of some rather 

 brightly polarizing mineral. They do not always occur in 

 solid areas, for portions of the space are free from them, 

 these isotropic portions running like veins through the mass. 

 These areas fill the greater part of the sections, but there is 

 always a narrow, irregular band along the margin which is 

 free from these minute inclusions, and is isotropic under 

 crossed nicols. The darker, central areas appear to be due 

 to a clouding, the nature of which could not be determined. 

 Besides these minute inclusions there are others scattered 

 through the slide, which have been mentioned in connection 

 with the hornblende. Some of the garnets contain here and 

 there, particularly along the isotropic borders, minute needles 

 of a yellowish to brownish mineral, with parallel extinction 

 and high refractive index, and giving high polarization col- 

 ors. This mineral is probably rutile. A few of these nee- 

 dles were seen in some of the hornblendes bordering the 

 garnets in which the inclusions are found, and some of the 

 needles were seen extending from the one mineral into the 

 other. There are rarely inclusions of large grains of rutile 

 and small hornblendes. 



