Finlayson. — Schists of Central Otago. 



75 



Composition. 

 The following analyses show the composition of these rocks : — 



99-37 99-29 100-00 100-39 95-89 



1. Chlorite - schist, Dunstan Ra. ; Anal., J. S. Maclaurin 

 (Bull. No. 1, N.Z. Geol. Surv., 1906, p. 42). 



2. Chlorite- schist, Gibbston ; Anal., A. M. Finlayson. 



3. Chlorite-schist, Klippe, Sweden ; quoted by Roth, Ge- 

 steinsanalejsen, 1884, p. 8). 



4. Epidote-schist from diabase, South Mountain, Pa. ; C. H. 

 Henderson, Trans. Amer. Inst. Min. Eng., xii, p. 82. 



5. Diabase, Point Bonita, Calif. ; F. L. Ransome, Bull. 

 Geol. Dept. Univ. Calif., i, 106. 



The features of the two Otago types are the low silica per- 

 centage, and the high proportions of lime, magnesia, and notably 

 titanium. These figures indicate a basic igneous rock. Analyses 

 3 and 4, of chlorite-schist and epidote-schist respectively, show 

 analogous features. No. 5, of a typical diabase, is inserted for 

 comparison, and shows close correspondence in respect of the 

 main constituents. 



Petrography. 



Under the microscope, type No. 1 (Plate XII, 2) shows a 

 mass of chlorite fibres and scales imbedded in elongated granules 

 of quartz, the structure being perfectly schistose. Rutile is 

 abundant in elongated crystals ; plagioclase and magnetite 

 are accessories, though the last is frequently very coarse and 

 strikingly developed in large and thickly clustered octahedra. 

 Calcite and epidote are very abundant, and the rock is sometimes 

 so highly epidotised as to constitute an epidote-schist. Some 

 specimens carry pyrite in large flattened cubes. The altera- 



