DALY. — AMPHIBOLES AND PYROXENES. 323 



abnormally high ; the optical angle is also unusual, for calculation shows 

 that it must be about 55°. Unfortunately, for reasons speciQed above, 

 the mineral cannot be separated and chemically analyzed. 



In the process of working out these illustrations, the author has come 

 to the conclusion that, with the proper safeguards, the method can be 

 safely applied to the amphiboles in general ; and that the pyroxenes can 

 be similarly treated. It may thus prove to have more than mere theo- 

 retical interest. 



