TERTIARY VOLCANIC ROCKS 259 



parasitic cone. Dr. Jensen describes the kenyte of the Skiiary as being character- 

 ised by a low content of TiOg, with mixch orthoclase and pure alkali-pyroxene, a 

 little olivine and magnetite, and a ground-mass as in trachytes. 



One of the most interesting spots for studying the relations of the lavas and 

 tufts of Mount Erebus is Cape Barne. At Cape Barne basic kenytes, like those 

 also represented at Turk's Head, are well developed. These are characterised by a 

 high content of TiO.,, with acid plagioclase felspar, titaniferous alkali j^yi'oxene, 

 much olivine and magnetite, and a tephritic ground mass. 



Sections have already been given showing the nature of the junction line between 

 the basic kenytes of Cape Barne and the magnetite basalts of the same locality. 

 These sections show that the magnetite basalts are strongly intrusive into this type 

 of kenyte. 



A remarkably interesting tuft' cone and the parasitic cone known as Mount Cis 

 have already been described in the chapter on Vulcanism. The rock of the tuft' cone is 

 basic and obviously tufaceous, consisting only of fragments of blackish-grey to light 

 grey porphyritic lavas. The fragments are mostly from 5 to 15 millimetres in 

 diameter. In addition there are a few fragments of micro-crystalline basic rocks, 

 much decomposed and reddened by hsematite, about 10 to 15 millimetres in diameter. 

 There are occasional angular fragments of a yellowish-brown friable rock resembling 

 palagonite tuft", also sprinkled by angular fragments of felspar. Dark included 

 fragments are rendered porphyritic by plagioclase felspar, probably mostly anortho- 

 clase with numerous glassy inclusions. These are set in a micro- crystalline base of 

 titaniferous augite, plagioclase, and magnetite. In some of the fragments the base 

 is glassy. The large 80 millimetre inclusion is a type of kenyte more acid than 

 that found at Cape Royds, and nearer to the type met with at the Skuary. 



The basalts of Cape Barne are described by Dr. Jensen as being either of the 

 variety poor in olivine, limburgite, in places basanitic, or magnetite basalts. 



The magnetite basalts of Cape Barne are somewhat remarkable rocks ; they 

 are also represented at Tent Island. Dr. Jensen considers them to be the most 

 diff'erentiated portions of the parent kenyte magna. They are formed chiefly of 

 basic labradorite accompanied by small rods of augite with corroded olivines, the 

 base being made ujo mainly of magnetite and dark isotropic glass. Dr. Jensen 

 considers that the magnetite has been one of the last minerals to form. 



Near Hut Point interesting representatives of the tephrite family are met with, 

 together with enstatite olivine ba.salt or basanite and limbui'gite. Limburgite and 

 limburgitic basalt are represented at Hut Point and at the adjacent Observation 

 Hill, while leucite tephrite occurs in situ at the top of Crater Hill. " This is a 

 reddish porous rock," says Dr. Jensen, " the vesicles of which are arranged in planes 

 or bands. The core of the specimen is dark, looking rather like a basalt, and has 

 small leucite and nosean phenocrysts of minophyric size studded through the aphanitic 

 base. The leucites are, under the microscope, seen to be altered to a mosaic of 



