Vol. 4] Thelen. — Thermal Conductivities of Certain Schists. 221 



tints and such identifications are always corroborated by the 

 characteristic undecomposed faces and by the Becke test. 



The titanite is veiy uniformly and plentifully distributed in 

 small rounded or rhombic shaped sections. 



The epidote occurs in small fragments very sparingly distrib- 

 uted. 



The apatite is very abundant in small idiomorphic crystals. 



The magnetite is all in fairly large grains. One cross-section 

 shows a maximum diameter of over 1 mm. 



The hematite occurs in a few blood-red blotches. 



Broad zones of strongly developed kaolinization permeate the 

 rock. There are no fissures observable along these zones and the 

 reason for their presence is not apparent. 



The Claucophane Schist. — This is a local schist from Berke- 

 ley. The rock is wholly crystalline. The structure corresponds 

 to the allotriomorphic of the igneous rocks. Foliated structure is 

 well developed. The constituent minerals are : — glaucophane, 

 lawsonite, acid feldspars, and epidote. 



Glaucophane makes up over 80 per cent of the rock. The 

 habit is elongated parallel to c. C-.c is less than 6 degrees. The 

 optical orientation is very easily determined by the pleochroic 

 colors These are as follows: C — sky blue to ultramarine blue; 

 b — reddish or bluish violet; a — yellowish to colorless (white). 



The individual crystals are small. The bottom slide contains 

 C of every crystal and 3 and b, or components of both promis- 

 cuously. Thus with the upper Nicol out, the tint of the rock as 

 a whole varies uniformly as the field is rotated. 



The side and end slides show a parallelism of the traces of 

 the c axes, but the axis itself niay lie in the plane of the slide 

 or make any angle with it. Thus many sections show the pris- 

 matic cleavage, many sections contain a and C, many contain 

 b and C. 



The structure of the glaucophane in the rock is then appar- 

 ently as follows: — all the longer axes (c) lie in planes parallel 

 to the bottom of the rock ; in each plane the c axes point in all 

 azimuths indifferently. There is no uniformity of orientation of 

 a and h whatever. 



