332 SoiifJicru Cross. 



Volcanic; rocks, as aliuiuly jioiiitcd out, tliu plionnlitic tiachytes present 

 striking' unal(»«,Mes with the ])h()!i()litic rocks of New Zealand. 



As far as it is ])ossihlc t() judge from tlie jtresent collection, the 

 ^eolt)<,'y of ^'i(•toria Land in its threefold character (Arcluean and 

 I'ahi'ozoic rocks, long uneventful period of terrestrial conditions, 

 lullctwed by recent volcanic eruptions) is similar to that of East 

 Africa and Southern India. Too much stress, however, must not 

 he laid on this a])])arent similarity, since so little is known of the 

 interior, the future exploration of which may possibly lead to the 

 discovery of fossiliferous IMesozoic rocks which may help to bridge 

 over the long interval between the Pala30zoic slates and the recent 

 l)asalts. 



■ EXPLANATION OF PLATE LIIL 



Microscope-sections of Antarctic Rocks. 



Fig. 1. — Plagioclase-olivine-augite-biotite rock. 



Finely-striated ]ilajiiocla8e felspars with iiatches of olivine (lai'ge irregular 



crystal uear tlie centre and smaller fragments), pale green augite (small 



fragments showing cleavage), and biotite. 

 Magnification, 10 diam., 2-in. obiectivc. 

 Fig. L'. — Biotite-hornblende-grauite with allanite. 



Two crystals of allanite are seen at the top, and a smaller lounded fragment 



below on the right. 

 Ma:_'nitication, 10 diam., 2-in. objective. 

 Fig. 3. — Kenyie-iike rock. 



At the top on the right is a crystal of anorthuclase showing the Hne twin- 



striations as seen between crossed uiculs; inniiediately below is a rounded 



fragment of red altered olivine; the other two phenocrysts are of augite with 



magnetite inclusions. 

 Ma-nitication, 18 diam., 1-in. objective. 

 Fig. 4. — I'honolitic trachyte. 



At the top on the left is a rounded crystal of yellow olivine with an inclusiiin 



of apatite and a border of a>girine-augite ; below is a phenocryst of anoriho- 



clase ; the dark shreds and patches in the gronndmass consist of a-girine- 



augite. 

 Magnification, 18 diam., 1-in. objective. 

 Fig. 5. — llurnbiei.de- basalt. 



The section shows small phenocrysts of basaltic-hornblende surrounded by a 



zone of magnetite, felspar laths, and rhombic sections of olivine in a glassy 



base. 

 Magnification, 18 diam., 1-in. objective. 

 Fig. (;. — 'i'ufl" with fragments of jierlitic kcnyte and basalt. 



Most of the secticm is occupied by a frav^ment of kcnyte showing perlitic 



structure; on the right is a fragment of glassy basalt. 

 Magnification, 35 dian)., ^-in. objective. 



