FROM THE MAINLAND OF SOUTH VICTORIA LAND 223 



Basic (Lamprophyric ?) Inclusions 



The granites ot South Victoria Land offer plentiful examples of basic inclu- 

 sions. 



The inclusions fall into two classes. The one is biotitic, the other hornblendic. 

 The former, though of common occurrence, is unimportant and can be quickly- 

 despatched. These are dark-coloured patches appearing at intervals in the face of 

 the granite. They are generally of but a few inches in diameter. The constituents are 

 the same as those of the granite, but the more basic minerals predominate. 



A slide of one of these patches from the Cape Irizar granite exhibits the following 

 characters : Even fine-grained, lacking the porphyritic orthoclases of the parent granite. 

 Its relations to the enclosing granite indicate it to be endogenous, and an early 

 crystallisation product. It is allotriomorphic granular ; grain size averages 1 mm. 

 Orthoch.se is present in small amount. Oligoclase and andesine predominate. Quartz 

 is plentiful. Biotite is abundant. Apatite and zircon are both much more concentrated 

 than in the granite. A few grains of sphene are also noted. This inclusion is, there- 

 fore, syenitic in character. 



Much more important are the hornblendic (dioritic) masses distributed through 

 the grey gneissic granite of Depot Island. These are sub-angular to rounded and vary 

 from a few inches to several feet in diameter. They weather out in relief on the cliff 

 faces and have undoubtedly solidified prior to their inclusion in the granite. Their 

 chemical composition indicates that they are related to the granite magma itself, and 

 it appears as if they are earlier lamprophyric separations, subsequently burst through 

 by the mother magma. 



These boulders are fairly uniform in texture, though frequently intersected by 

 coarser veins of the same constituents. The arrangement of these veins is pegmatitic 

 and the distribution of the minerals in the veins is uneven. Many of the veins pass 

 out of the inclusions into the gneiss, and show their period of formation to have 

 followed upon the solidification of the enclosing gneiss. The constituent * minerals are 

 biotite, hornblende, plagioclase, quartz, and accessories. The latter include abundance 

 of a reddish-brown sphene. 



Unfortunately our specimens were unrecoveredf from the depot and microscopic and 

 chemical analysis cannot be effected. There seems to be no doubt, however, but that 

 this is one of a dioritic class well represented in our collections. Examples of the 

 latter occur as erratics weighing as much as one hundredweight on Ross Island ; they 

 are also found in the Ferrar Glacier collections, as erratics at Cape Irizar, and in the 

 vicinity of Mount Larsen. 



Ferrar describesj masses of hornblendic rock occurring in the pink granite of the 

 Kukri Hills as metamorphosed inclusions of the intruded dolerites. If this is so it 

 seems likely that there exists no relation between these inclusions and those of Depot 

 Island, for the analysis of the supposedly similar hornblendic rocks to be described 

 later in no way corresponds with that of a dolerite. 



Further, Ferrar has noted the pink granite of the Cathedral Rocks || gradually 

 passing over to a coarse-grained diorite similar in most respects to the Depot Island 

 inclusions. 



This evidence favours the origin of the basic boulders in the Depot Island gneiss 

 as earlier solidified differentiation products from the granite magma itself 



* From field notes. 



f Since writing this the specimens have been recovered by the Scott Expedition of 1912. For 

 description see Paper following by L. A. Cotton. — D.M., 1916. 



t Loc. cit., pp. 36 and 128. II hoc. cit., 36. 



