FROM THE MAINLAND OF SOUTH VICTORIA LAND 209 



THE IGNEOUS ROCKS 



Ferrar and Prior have described a large series of igneous rocks from South Victoria 

 Land. Most prominent amongst these are granites, mostly very ancient, dolerites 

 of intermediate age, and a recent alkali series of intermediate and basic rocks. None 

 of the latter occur in situ on the mainland in the region within the scope of these col- 

 lections. Erratic blocks are, however, frequent. Ferrar distinguishes an older and a 

 younger granite. The older granites are grey and intrude an ancient metamorphic 

 series of gneisses and schists. The younger granites are pink in colour, and according 

 to Ferrar intrude the dolerite sills which are themselves younger than the Beacon 

 Sandstone. More information on the subject of the relative ages of the pink granite 

 and the dolerite is desirable, for our observations have shown that there do exist grey 

 granites of the same age as some pink granites. 



Ferrar also met with diorites, syenites, gabbros, and lamprophyric, aplitic, and 

 pegmatitic rocks. 



For convenience I have recognised the following groups : 



The Granites and their associated Dyke Rocks. The latter include porphyrites, 

 aplites, pegmatites, and lamprophyres. Granites of several ages are recognised. 



The Diorites. These doubtless correspond in age with some of the granites. 



The Gabbros. Most of those classified under this heading are believed to be older 

 than the " dolerites " ; others may be special phases of the latter. 



The Dolerites. Included herein are a variety of closely similar types all of the 

 same period, intrusive in the Beacon Sandstone formation, and therefore comparatively 

 young. They appear to belong to the one great intrusive act illustrated by the dolerites 

 of Tasmania. They range over an enormous area of Antarctica.* 



The Recent Volcanic Series. Rocks of this series are of tertiary and recent age and 

 are exemplified in the extravasations of Mount Erebus. It is doubtful whether any 

 outpourings of this class have taken place on the mainland proper within the area 

 embraced by these collections.^ 



THE GRANITES AND ASSOCIATED DYKE ROCKS 



Granites and their dynamometamorphic equivalents form a large part of the exposed 

 areas, and consequently the collections are rich therein. 



The majority of the specimens collected are coarse-grained and porphyritic with large 

 pink orthoclase crystals. Very large outcrops of this granite are known to occur between 

 75° 50' S. lat. to 78° S. lat. It is probable, however, that the areas occupied by grey 

 granites predominate. Petrological comparisons and certain field evidence indicates 

 a relationship between the pink granites and certain of the grey granites. This re- 

 lationship is closer than is likely to be the case if they belong to two widely separated 

 periods. This, however, appears to be the case with others of the grey granites as 

 indicated by Ferrar' s field evidence.! 



In any case it is certain that granites older than the pink felspar granites exist, 

 for some of the granite-gneisses are plainly of such antiquity. It is significant that 

 of the arkoses, so frequent amongst the sedimentary rocks, none have yet been met 

 containing pink felspars. 



* These are described in detail elsewhere in this volume by W. N. Benson, B.Sc. 

 f Examples of such rocks have been brought to light by the recent Scott Expedition. — D. M., 

 1916. %Z. Loc - ciL > P« 36 - 



