and Igneous Rocks of Ensay. 81 





No. 4. — Quaetz- 



■Schist. 





Si.O, 



• I • • i • 



, , , 



74-27 



Al.O, 



... ... 



. . . 



1314 



Fe..,0 3 



... ... 



. . . 



101 



Fe.O 



... ... 



• . . 



211 



Ca.0 



... ... 





1-33 



Mg.O 



..< 





2-56 



K o 



... . . , 





1-49 



Na. 2 



... ... 





2-91 



H 2 







213 





100-95 



Hygroscopic moisture ... -28 



Specific gravity ... ... 2'85 



I have not attempted to calculate the mineral percentages 

 in this schist. Without knowing the composition of the 

 alteration-products in it, the results to be so obtained would 

 be, in a great measure, hypothetical. 



The coarsely crystalline part of this rock (b in sketch) is a 

 crystalline-granular compound of reddish felspar, quartz, 

 chlorite, and alkali-mica. Under the microscope I found it 

 to be as follows :— 



The felspars are mostly triclinic, with low obscuration 

 angles. None are perfect in form, but they are broken 

 rather than rounded off. They give evidence of force with 

 which they have been driven against each other during the 

 movement of the mass. The felspars are much altered to 

 mica, some of the plates being of sufficient size to be 

 examined under the microscope, and I found them to react 

 in all respects like one of the alkali-micas. 



Some few of these felspars are not striated, and may 

 possibly be orthoclase. 



Chlorite occurs, representing magnesia-mica, and there is 

 an alkali-mica, both in aggregates of small scales and in 

 larger crystals. 



The quartz is filled with innumerable minute fluid 

 cavities, without bubbles, and also with greenish microliths r 

 in flakes, whose nature I am unable to conjecture, unless 

 they are chlorite. 



I observed, also, as showing the mechanical changes which 

 have occurred in this rock, that several crystals of felspar 

 had been broken across in the same line, together with the 

 interstitial quartz between them. The fissure thus formed 



