150 «• T. PRIOR. 



Victoria Land,^ and viuder III the analysis of a glassy dolerite 

 from Londorf, Vogelsgebirge.- 



In connection with the dolerites a peculiar hybrid rock is 

 worthy of description. It is intrusive in granite about five 

 miles above the crossing of the Mapamulo and Isidumbeni 

 road over the Umvoti Kiver, Natal. The specimen (226) of 

 this rock in the collection is labelled "basalt which has 

 absorbed granite, only leaving porphyritic crystals of felspar." 

 It has a minette-like appearance, and shows under the , 

 microscope (see PI. VI, fig. 1) small reddish-brown biotites 

 and pale green augites, plentifully and evenly distributed in 

 a felspar mosaic. With the augite is associated a little faintly 

 pleochroic enstatite ; the felspars are mainly of oligoclase, 

 showing albite twinning, and having a refraction slightly 

 higher than that of Canada-balsam. There are present also 

 included patches of micro-pegmatitic material (quartz de 

 corrosion) similar to that in the granite associated with the 

 rock, and large crystals of oligoclase showing symmetrical 

 extinctions about the twin-lamell« of about 10°, and containing 

 small blebs of pale-green augite, grains of magnetite, and 

 rods of biotite. A few quartz grains, occasionally micro- 

 pegmatitically intergrown with felspar, are present in the 

 mosaic; grains of magnetite are only very sparingly distri- 

 buted. All the constituents are clear and fairly free from 

 inclusions. Another specimen (22.5), from the same locality, 

 shows the junction of a coarse-grained granite with a some- 

 what similar rock to the above, except that in this case a 

 green to yellow hornblende takes the place of the augite. 

 This rock bears some resemblance to the hybrid rocks from 

 Skye described by Marker.^ 



The o-ranite which is said to occur as " seams " in the 

 hybrid rock is a coarse-grained rock consisting of large ortho- 

 clases and microperthites with some oligoclase in a coarse 



' L.c, vol. i, ' Geology,' p. 137. 



2 Streng, 'Neues Jalirb. f. Min., etc.,' 1888 (2), p. 217. 

 ^ Harker, '" The Tertiary Igneous Rocks of Skye," ' Mem. Geol. 

 Sxn-v.,' 1904, p. 182. 



