38 Washington — Study of the Glaucophane Schists. 



red garnets, the whole being rather fine-grained and traversed 

 by veins of quartz, which were carefully avoided in the pieces 

 chosen for analysis. 



Under the microscope the glaucophane appears in long 

 crystals, with fringed ends, of the normal gray-blue color and 

 pleochroism, the blue being deeper at the borders. The 

 epidote is slightly greenish yellow, in elongated crystals, and 

 much broken. It is sometimes difficult to distinguish it from 

 the diallage, which occurs in generally larger crystals and less 

 green in color. The garnets are almost colorless and much 

 cracked. The flakes of mica present the usual characters 

 of muscovite, but they must be referred to the soda-mica 

 paragonite, on account of the mere trace of K 2 which the 

 analysis reveals. Apart from the veins, grains of quartz are 

 fairly abundant, scattered through the other constituents and 

 interstitial. Small brown titanites are seen here and there, a 

 little chlorite is present, and also grains of an apparently 

 alkaline feldspar. 



Through the kindness of Prof. Lawson and Dr. Ransome, I 

 have been enabled to study specimens and sections of the 

 lawsonite-bearing schists of California, but have been unable to 

 find any of this interesting mineral in the rocks of Syra. 



The analysis (No. Ill, below) shows a much higher percent- 

 age of Si0 2 than the preceding, slightly lower A1 2 3 and Fe 2 3 , 

 the same MgO and FeO and K 2 0, with lower CaO and higher 

 Na 2 0. In nearly all respects, with the notable exception of 

 the Na 2 0, it is transitional between the analyses of the more 

 basic rock and that of the quartz-glaucophane schist to be given 

 presently, and this intermediate character is quite consonant 

 with its complex and transitional mineral composition. In its 

 general features it resembles the analyses of many diorites, and 

 it may be mentioned here that this analysis is quite unique 

 among the dozen or so given in this paper. 



The mineral composition being so complex, any satisfactory 

 calculation of the relative amounts of the component minerals 

 is difficult, and would be arbitrary. 



Quartz-glaucophane Schist. — It has already been said that 

 von Foullon and Goldschmidt divided the glaucophane schists 

 of Syra into the two groups in which the blue hornblende was 

 associated with either epidote or mica. While this is in gen- 

 eral true, and in correspondence with the megascopical appear- 

 ance of the rocks, yet it does not recognize fully enough the 

 fact that the mica-glaucophane schists tend to become highly 

 acid through the increase in quartz and decrease in mica. 

 I have therefore referred some of my specimens to a 

 third group of quartz-glaucophane schists, in which the mica, 

 while present, and prominent in the hand specimen, yet is in 



