226 PETROLOGY OF ROCK COLLECTIONS 



Chemico-mineralogical Classification : Class 2, Order 5, Rang 4, Sub-rang 3 (Hessose). 



BlOTITE-HoRNBLENDE DlORITE ; CAPE IRIZAR 



An erratic specimen from Cape Irizar is similar to the first of the diorites described 

 above. In this, however, the grain size is somewhat larger and the constituents show 

 a greater tendency to panidiomorphism. 



Microscopic Characters. The plagioclases show albite, carlsbad, and pericline twins 

 and are very strongly zoned ; the zoning, which is from andesine to oligoclase, is often 

 repeated a second time. Hornblende is more abundant than biotite and the prisms 

 reach 6 mm. in length. The biotite is often enclosed within the hornblende. Quartz 

 is more prominent than usual and often surrounding many crystals in poikilitic fashion. 

 Sphene appears in scattered grey grains ; in the hand-specimen these are yellowish- 

 brown. Apatite prisms are abundant. Zircon, occasional rods ; one of these is 

 surrounded by a halo. 



A rock of this class occurs amongst our collection from Dunlop Island, on the 

 coast-line farther to the south. 



Amongst the collection from the Ferrar Glacier Moraines are two very striking 

 specimens of sphene-bearing amphibolites allied in composition to the preceding. 



Sphene-bearing Amphibolite, Ferrar Glacier Moraines. This is a coarse-granular 

 speckled rock composed of dark amphibole, white plagioclase, quartz, flakes of biotite. 

 and grains of clove-brown sphene. 



Microscopic Characters. Hypidiomorphic -granular texture. Quartz occurs in large 

 and small pieces. The plagioclase have the composition of andesine. Amphibole is 

 the most abundant constituent ; it is uralitic. Sphene and apatite are unusually 

 abundant. Magnetite grains are rarer. 



Another specimen of this class, though finer grained, comes from Dry Valley (Fig. 2, 

 Plate IV). 



Under the subject of the lamprophyres of the granite following reference has been 

 made to the occurrence of a large outcrop of diorite in connection with the pink granite 

 at Cathedral Rocks, Ferrar Glacier, as described by Ferrar. The diorites described in 

 these pages are similar in composition, though differing somewhat in mineral contents. 

 The characters of these rocks are not typical of normal diorites but are suggestive of 

 lamprophyric separations. It is significant that their composition is very similar to 

 the kersantite dykes met with intersecting the granites ; this is illustrated in the 

 following tabulated analyses : 



I. Diorite from Camp Lake at the foot of the Larsen Glacier. 



Analyst : A. B. Walkom, B.Sc. 

 II. Diorite from moraine about 20 miles south-east of Mount Larsen. 

 Analyst : A. B. Walkom, B.Sc. 



III. Diorite from Cathedral Rocks, Ferrar Glacier. 



Analyst : Dr. Prior. 



IV. Kersantite crossing pink granite, Cape Irizar. 



Analyst : A. B. Walkom, B.Sc. 



