234 PETROLOGY OF ROCK COLLECTIONS 



Figure 3. — A microphotograph, under crossed nicols ( x 16 diameters) of the even- 

 grained light-grey granite from the Lower Glacial Depot, Beardmore Glacier. 

 The principal minerals present are quartz, anorthoclase, microcline, oligoclase, 

 biotite, and muscovite. Clear blebs of quartz are seen included in the felspar. 



Figure 4. — A microphotograph ( x 16 diameters) of the pink granite from Cape Irizar. 

 The minerals present in the photograph are clear quartz, dusty anorthoclase, a 

 small amount of plagioclase, biotite, and hornblende. Biotite-hornblende granite. 



Figure 5. — The same under crossed nicols ( x 16 diameters). The anorthoclase and 

 plagioclase can now be distinguished by the twin lamella?. 



Figure 6. — A microphotograph ( x 16 diameters) of the grey aplitic granite porphyry 

 from Cape Irizar. This particular slide illustrates the aplitic base which pre- 

 dominates over the porphyritic material. In the photograph, the dusty felspar 

 is readily distinguished from the clear quartz. The dark minerals are biotite and 

 hornblende. 



Figure 7. — A microphotograph ( x 17 diameters) of a hornblendic aplitic granite 

 porphyry occurring as an erratic at Cape Irizar. The porphyritic light-coloured 

 individuals are zoned plagioclases. Idiomorphic hornblendes are abundant. 



Figure 8. — A microphotograph ( x 16 diameters) of a pink aplitic granite porphyry 

 occurring, in situ, amongst the granites at Cape Irizar. This comes from another 

 portion of the same outcrop as Fig. 6. The porphyritic individuals are plagioclase. 



Figure 9. — A microphotograph, under crossed nicols ( x 17 diameters) of a pink- 

 coloured graphic aplite occurring as an erratic at Cape Irizar. Note the graphic- 

 quartz and orthoclase surrounding small porphyritic oligoclases. 



PLATE IV 



Figure I. — A microphotograph ( x 18 diameters) of sphene diorite from the moraine 

 twenty miles south-east of Mount Larsen. The minerals present visible in the 

 photograph are quartz, plagioclase, biotite, hornblende, sphene, and apatite. A 

 sphene-biotite-hornblende diorite. 



Figure 2. — A microphotograph (x 16 diameters) of a sphene-bearing amphibolite 

 collected as an erratic from the Dry Valley Moraines, McMurdo Sound. This 

 rock is an altered gabbro or basic diorite, and is notable for the amount of clove- 

 brown sphene which it contains. The larger dark areas in the photograph are 

 uralite ; smaller fragments of biotite are numerous. The felspar is of the com- 

 position of andesine and oligoclase. Grains of quartz are not infrequent. Sphene 

 and apatite are comparatively abundant. 



Figure 3. — A microphotograph under crossed nicols ( x 18 diameters) of a saccharoidal 

 marble found as an erratic at the Stranded Moraines, McMurdo Sound. Black 

 spots of graphite appear amongst the granular calcite. 



Figure 4. — A photograph of a hand-specimen of the pink granite from Cape Irizar 

 showing on the left-hand side of the photograph a junction with a black kersantite 

 vein ; x \h diameter. 



Figure 5. — A photograph of a hand-specimen of the sphene diorite found as an erratic 

 at a moraine on the ice-fringe twenty miles south-east of Mount Larsen ; x \ dia- 

 meter. This rock is notable for the amount of beeswax-yellow sphene which it 

 contains. Fig. 1 is a microphotograph of the same rock. 



