BY H. I. JENSEN. 119 



(5) Nomenclature : Aplite. 



(6) Remarks. — The magma which gave origin to this rock 

 must have been very alkaline, not unlike the more recent tra- 

 chytes. The amount of albite is abundant proof of this. 



Sp.No.59. Ortho-Gneiss. Loc: Fife's Range, Delaney's Ck. 



i. The handspecimen is brownish and shows a gneissic lamina- 

 tion with augens of quartz. 



ii. (1) Texture : a noncrystalline even-grained rock whose con- 

 stituents are of a medium grain-size and exhibit a foliated 

 structure. The fabric is allotriomorphic granular, and banded. 



(2) Constituents. — Essential, (i.) orthoclase, (ii.) quartz, (iii.) 

 biotite; minute, (iv.) muscovite. (v.) apatite, (vi.) dusty magnetite. 



(3) Origin and name — This rock is a granitic vein or dyke 

 which has undergone intense rnetamorphism with the adjoining 

 sedimentary rocks. The most suitable name is therefore Ortho- 

 gneiss. 



Other closely related gneisses, some of decidedly uneven and 

 variable grain-size, occur on Fife's Range (Sp. No.56 of my collec- 

 tion). 



Epi-diorite. Loc: the Jimnah Goldfield, near Woodford. 

 ( Plate xi. fig 6). 



The section was made from a specimen collected by Mr. J. M. 

 Newman, B. E. It is a tine-grained black rock. 



Microscopic examination. — (1) Texture : (a) noncrystalline,. 

 (b) variable grain-size in specimen, but the greater part of the 

 slide examined was even and fine-grained, (c) hypidiomorphic 

 granular to panidiomorphic granular fabric with a schlieric 

 texture, similar materials tending to arrange themselves in bands. 



(.2) Constituents. — Essential (1) plagioclase, (2) green horn- 

 blende, (3) uralite : Accessories : — (4) magnetite, (5) quartz. 



(3) The plagioclase exhibits low extinction angles, but has a 

 greater refractive index than Canada Balsam. It is twinned in 

 accordance with the Carlsbad and Albite laws, and occurs in 

 idiomorphic crystals of small size. It appears to be andesine. 

 The hornblende is a fibrous actinolite with straight extinction, 



